"Used Beer Department” is a jocular restroom sign that has been printed on many images. “Two Shake Maximum” is sometimes added.

“Used beer department” was printed in The Daily Telegraph (Columbus, NE) on August 30, 1939. “On the wall was painted in large letters with a pointing hand: ‘To the Used Beer Department’” was printed in the book Maryland Main and the Eastern Shore (1942) by Hulbert Footner. “‘USED BEER DEPARTMENT’ August 1942. ‘Midway, Bingham County, Idaho. Sanitary facilities.’ Medium-format nitrate negative by Russell Lee for the Office of War Information | Shorpy Old Photos | Photo Sharing https://shorpy.com/node/25951” was posted on Twitter by Cigar Heid on October 30, 2020.

“Two shake maximum” ("USED BEER DEPARTMENT Two Shake Maximim” is shown on a sign over a urinal) was posted on Twitter by J🐒🚹 on January 20, 2013. “‘Used Beer Department - Two Shake Maximum’ best bathroom sign ive ever seen” was posted on Twitter by Spencer Rohlfs on January 28, 2014.

“Used Coffee Department” is a similar term.


Newspapers.com
30 August 1939, The Daily Telegraph (Columbus, NE), “Tuning In On Your Neighbors” by Jack Kintzi, pg. 1, col. 2:
In the more modest places they label those rooms plainly as “Ladies” and “Gents.” The coyer establishments list them as for “Bucks” and “Does,” and “Pa” and “Ma.”

But at Shorty’s place in Clarks the sign over the used beer department exclaims with refreshing simplicity and feeling—“I’ve Found It!”

Google Books
Maryland Main and the Eastern Shore
By Hulbert Footner
New York, NY: D. Appleton-Century Co.
1942
Pg. 184:
The porch roof leaked so plentifully we were driven inside the building, and we called for beer. On the wall was painted in large letters with a pointing hand: “To the Used Beer Department.” “What is the used beer department?” I asked of the little village girl who brought the beer, and then I saw the point and blushed. She was not in the least discomposed, “The Gents’ toilet.” Oxford humor.

Google Books
Tangleweed
By George William Willis
Garden City, NY: Doubleday, Oran, Incorporated
1943
Pg. 137:
They talked about Monty for a while, and then she excused herself. “Got to see the used-beer department,” she said.

Google Books
Florida Cruise
By Norman Alan Hill
Baltimore, MD: George W. King Printing Co.
1945
Pg. 295:
The Skipper made a special note in his log of a painted notation on a Chic Sale door overhanging the water at a nearby flimsy pier—“Used beer department”.

Google Books
Galaxy Magazine (Science fiction.—ed.)
Volume 9, Issues 1-4
1954
Pg. 90:
The used beer department is down those steps over there.

Google Books
Practice Makes Perfect
By Edward Vernon
New York, NY: St. Martin’s Press
1977
Pg. 26:
He might have just emptied his beer-glass and discovered the need to refill it or to make a trip to the used—beer department.

Google Groups: tor.eats
Review: Hotters (Try # 2)
Alan Marshall
Apr 15, 1997, 3:00:00 AM
(...)
Near the washroom the sign reads “Used Beer Department”.

Google Groups: rec.games.pinball
Coka Cola theme Pinball???? 
Homebru
Oct 27, 2001, 1:27:17 PM
Sign over toilet:
“Used beer dept.”

Google Books
Vice Slang
By Tom Dalzell and ‎Terry Victor
New York, NY: Routledge
2007
Pg. 194:
used beer department noun
a toilet US, 1995 Modified to ‘used coffee department’ and the like for office settings.

Twitter
Brett
@brett_makes
Replying to @goodbeershow
@goodbeershow The best brewpub bathrooms are the ones labeled “Used Beer Department”
8:51 AM · Apr 30, 2009

Twitter
DennisFMaloney
@DennisFMaloney
Sign over a restroom in a restaurant: “Used beer department.”
8:27 AM · Jul 16, 2009

Twitter
Ian Rice
@CateyeMinty
RT @GuitarDragon: “‘Sign over a restroom in a restaurant: “Used beer department.’” || MAKES SENSE
4:36 PM · Jan 21, 2010

Twitter
Slau Halatyn
@SlauBeSharp
LOL Best sign on men’s room door at Ulrich Tavern: “Used Beer Department”
10:32 AM · Jun 26, 2010

Twitter
jsaquella
@jsaquella
Replying to @KKurzNHL
@kpkurz99 @JamieApody I was visiting the used beer department and came back to a commercial LOL
10:25 PM · Oct 10, 2010

Twitter
Cate
@Catepics
Love the ad where the men’s toilet in the pub is called “The Used Beer Department.”
3:31 AM · Dec 7, 2010

Twitter
ccs
@niceninja
@veteranairborne You know you’re in big trouble when you frequent a bar that has an arrow to the “used beer department”
5:31 PM · Mar 1, 2011

Twitter
Lauren Billings
@Lolozilla
Bars that call bathrooms “Used Beer Department” = ick. [Why yes, I am revising at the pub at noon on a Monday].
3:00 PM · Dec 19, 2011

Twitter
Robin
@RedRockRobin
The brewery I’m at has a “used beer department”
10:42 PM · Jan 24, 2012

Twitter
Kristen Brooks
@kristenly2
Sign above the bathroom door says “used beer department” 😖😷
5:03 PM · Aug 6, 2012

Twitter
J🐒🚹
@FatMatDamon
“Two shake maximum.”
("USED BEER DEPARTMENT Two Shake Maximim” is shown on a sign over a urinal.—ed.)
9:15 PM · Jan 20, 2013

Twitter
Phill Gillespie
@PhillGillespie
Best Gents Toilets sign ever! Or rather, best “Used Beer Dept.” sign… Hugely impressed with The Porterhouse, Br…
(The sign is shown.—ed.)
2:36 PM · Apr 8, 2013

Twitter
Amy Novotny
@novotnyamy
“Used Beer Department”...aka, the restrooms! #sillysigns #wapitibar http://instagram.com/p/cQUInVq2fG/
11:52 PM · Jul 26, 2013

Twitter
Spencer Rohlfs
@spencerr11
“Used Beer Department - Two Shake Maximum” best bathroom sign ive ever seen
10:26 PM · Jan 28, 2014

Twitter
The Beez
@ambeezy10
The bathroom at this brewery is called the “used beer department.” I like it. #GreatBasin
5:48 PM · Nov 2, 2014

Twitter
Wade
@staticsan
@TheFeedSBS I was thinking of the term “used beer department”.
6:20 AM · Jul 6, 2015

Twitter
Ghost Bear 1981
@ghostbear1981
Replying to @DPRGuru @LovesPampers and @DiaperMates
Make one that says “Used Beer Department” with arrow pointing down - it’s for the front of the diaper....
9:24 AM · Jun 25, 2017

Twitter
Adrian Walters
@walters_adrian
Replying to @JohnKuczaj and @atomicshop
The gents’ bathroom at a pub I know in Yorkshire (UK) used to have a sign that said “Used Beer Department”
9:28 AM · Jul 19, 2017

Twitter
Jon W
@JonW_67
I couldn’t find the loos in the restaurant. The waiter helpfully pointed to the sign: “Used Beer Department”...
3:19 PM · May 15, 2018

Twitter
Teacher Fabio Emerim
@dicas_de_ingles
7 apelidos para WC inglês:
1 - altar
2 - can
3 - head
4 - throne
5 - throne room
6 - used-beer department
7 - shithouse
8:03 PM · Nov 7, 2019

Twitter
Cigar Heid
@Cigar_Heid
Something we all need sooner or later...,
“USED BEER DEPARTMENT”
August 1942. “Midway, Bingham County, Idaho. Sanitary facilities.” Medium-format nitrate negative by Russell Lee for the Office of War Information | Shorpy Old Photos | Photo Sharing https://shorpy.com/node/25951
4:39 PM · Oct 30, 2020

Twitter
John Edwin Mason
@johnedwinmason
“Used Beer Department. Her, His.”
(Russell Lee/FSA: Midway, Bingham County, Idaho. Sanitary facilities. 1942)
9:52 PM · Nov 9, 2020

Twitter
Thaddeus Longmire
@5ininseam
I will henceforth be referring to taking a piss as going to the used beer department
8:30 PM · Sep 9, 2022

Twitter
Iain (or John) Howieson
@John_Howieson
Replying to @kbdaly2468
I have a friend who always refers to the gents’ toilet in any pub as “the used beer department”.
3:45 PM · Nov 10, 2022