Trans people make up less than 1% of the US population. (It's around 0.6%) The numbers vary since not everyone has transitioned.
Assuming half (0.3%) are in the women's bathrooms, you're only coming across a trans person every 334 people. The amount of trans people that commit sexual assault is so low, that you can't even get a solid number.
Also, you're stupid if you think rapists are going to follow the sign on a bathroom.
Lastly, most sexual predators are not trans.