Like any old wise tales?
They are old "wive's" tales, and not old wise tales. They aren't wise, and they aren't reliable, but they can be fun. Oh well. Ultrasound is your best bet.
If your mare is overdue by a month its a stud colt ..... ALWAYS hear that one. So far it has a myth to its madness. As all of our mares seem to be a few weeks late are having studcolts ..... but I don't truely believe that all the way.
I have also heard of the nail test. You tie a nail to a long piece of horse hair, and hold it above the mare's back . The nail begins to move in a circle for a filly, or back and forth for a colt.
There are lots of old wise tales but none of them are 100% true.
Best to just get an ultrasound unless you want to be surprised!!
I haven't heard of any that will actually work. Either get an ultrasound or wait and find out!