If the plural form of a noun ends in -s (as it usually does) then just an apostrophy is added:
The dogs' food (but: The dog's food if it is only one dog).
If the plural form of a noun does not end in -s (these would be the older and today irregular plural forms), then you add an apostrophy AND also a genitive -s:
0Yes, the Mens Room can be a proper noun, if you want to say it is a specific place. (See some cool Mens Room murals by googling those words)02br 02br 00So we can change the orginal sentence to "men's lockeroom or men's lounge. The intent is to show the possessive form of the word men.0-
0Hi guys,02br 02br 01b00Mens Room02b00 should really be written as01b00 Men01font00'02font00s Room02b00. It's just that the people who write signs sometimes are not interested in grammar or else feel that apostrophes make their signs seem more cluttered, less elegant.02br 02br