I've been riding sola single/female since october '03 in Mexico, central america, save for 1 month and not so much as a squeak, well while I'm on the bike anyway, (A few cat calls when off) think Colesyboy is right in saying the bike brings on some extra respect.
I´m not in the 20 30 age group anymore and that makes a difference. Had a policeman get really aggitated with me when i pulled off road in a downpour to put on dry suit, was frothing at the mouth infact, when he finally twiged i was woman, it was comical the quick turn around in attitude.
Also i had heard of how fello riders get persistant hassle at borders to use guides etc. every time i've pulled up a really firm no thank you and they disappear. I came to the conclusion that its not macho to get confrontational with a woman, unless you are out to give her other kind of grief.
And i reckomend Honduras and Nicuragua also.
Over all i have been very pleasantly surprised at the honesty and attitude of the general public in this part of the world