I'd have to agree with what old&slow said. The extra info would confuse the heck out of most people. I've run into plenty of people looking at a 45 Colt ammo and 45 ACP ammo trying to figure out which one they need to buy. I've had people try and sell me ammo at the range because they bought the wrong stuff - 357 Sig instead of 357 Mag.

I'd be willing to bet any government mandated signage on ammo would be something similar to what's a cigarettes.

Anyone interested enough can view any of the 100's of ammo tests online. Luckygunner has a pretty good comparison of a large variety of common handgun rounds. A chronograph will also tell you velocity out of your gun which is all that matters.