I've had a few instances of ugly girls approaching/hitting on me usually when they've had enough to drink and can muster up the courage haha. Other than that I usually catch a few coy glances and mild flirting but never being outright approached. Most women are cowards and take rejection extremely bad, so they'd rather sit and let the guy do most of the work.
If we're talking random occurences then its more than likely a compliment that women generally find you attractive and a few of them just so happened to have the balls (or ovaries?) to break girl-code and pursue you. They seem to take it hard when you don't pursue them back, to them its a rejection and I've had women who've dropped hints go stone cold on me when I wouldn't take their bait.
OTOH, if ugly/fat women are consistently hitting on you in a very dominant manner then you're probably giving off submissive vibes. I usually think of a very skinny non-threatening dude, most of them are the biggest fat chick magnets for that very reason.
I highly doubt the latter is the case for you.