The German plural is not very often an "s" added to a word (rather few times this is actually the case), so that helps.
For example, while it would be "house" and "houses" in English, in German it would read "Haus" and "Häus
er". Or for "tree -
trees", it's "Baum -
Bäume". In cases where there's indeed a "s" used for a plural (e.g. "Auto
s" for "cars"), common sense dictates the understanding in so far that another noun has to follow for a possessive case to exist which cannot be the case for plural use. (However, a plural can follow a possessive case.) See: "The car
's color(s)" translates to "Die Farbe( n)
des Auto
s" with the latter being a formal example of the grammatic case called "Genitiv", implying possessive attributes.
Easy.