Male or Female at sight?

I have yet to go and have my boa sexed by my vet. I consider my snake a he, because i'm told with most of the red tail boas, at least the one i have ( i got from petco ;/ ) they're mostly males? True or not, not the issue. He's about 2 years of age. Is there any way by just looking at my RTB and noticing something that is different between the males and females? I'd go to the vet, and i do plan on it here in the next couple of months, i just can't afford it right now, so i figured i'd ask if there is any difference between sex's that stands out. I once heard something about the tail? But not sure what it was.

Anything? Please and Thank you!

As adults, you could tell with a moderate degree of certainty just based on size, but keep in mind there are always small girls and huge boys. Other than that, no visble way that is really reliable. The tail check I think is much more telling in colubrids.