[Thanks to the mod who deleted the other thread. While I do like being mischievous, I don't like being destructive like that. Sorry for the trouble]
Learn to use apostrophes!
There is NO apostrophe in plurals. (mobs not mob's)
There IS an apostrophe in contractions. ("it's" for "it is", "don't" for "do not")
There is NO apostrophe for the neuter possessive, its. It's just like his or hers, you don't put one before the s.
There IS an apostrophe for other possessives. If it doesn't end in an s, generally you add an 's. If it does end in an s, generally you add an apostrophe AFTER the s.
Really, this isn't that hard. If you use proper grammar and spelling, people will think you're a dumbass because of what you say, not how you say it!
Next time: your, you're, and ur!