Produces an egg sac or the exuvia reveals spermathecae and/or uterus externus. Mature females are typically more heavily bodied than their male counterparts, although body shape and size is not a reliable way to sex your spider.
Molts into maturity with tibial apophysis and/or palpal emboli or exuvia does not reveal spermathecae and/or uterus externus. Only mature males will have tibial apophysis and/or palpal emboli. Both females and immature males will not have these features. Once a male matures, he will likely die before molting again. Also, some species do not have tibial apophysis at maturity.
When I look at a molted exuvia, how can I tell that my spider is female / male?
When examining an exuvia, it always helps to have some type of magnifying device if the molt is very small (under 3"). You will look at the area between the booklungs.
If the skin is folded, you can briefly soak it in water with a few drops of liquid soap to make it moist enough to open up. Once the skin is opened, look closely at the area shown in the picture.
If it is a female, you will see a "flap" (the uterus externus), the bursa copulatrix, and possibly the spermathecae. If it is male, you will not see a uterus externus, bursa copulatrix, or spermathecae. Each of the following examples is female.
It is also possible, with practice, to sex your tarantula ventrally with a high degree of accuracy. You can read more about ventral sexing here.