Hmm, I don't think so. LOL! Sometimes you can tell a bit in their face or eyes, but that's not 100% accurate usually, haha. :P
& stallions have their testicles, unlike geldings. Geldings come from 'geld', like how you geld a stallion so he can't breed (just like they neuter dogs & such). ;)
If its a really tall horse and you are short you don't have to bend over.
I can usually tell without bending. Males penises are more forward on the belly. You can usually see it without bending over. Mares of course have nothing on the belly just teats, usually high up and back between the legs.
Here is the best image I could find:
See the penis hanging at mid belly?
Here is a mare, the belly is smooth:
You can always tell by looking under the tail. The male has one hole (the anus) and a mare has 2 (the anus and the vulva)
Hope this helps.