It's my understanding that an apostrophe stands in for a missing letter. The apostrophe in "it's" takes the place of the missing "i" in "it is". Ol' actually means "old", etc.
This means that the word "don't" could actually mean "donut"! Yum.
I wonder if I should open my own store using this cute way of spelling doughnut?
Hmm, probably not.