If you’re asking for a cast-signed playbill, your package should contain:
1 letter describing your request
1 SASE (Self-Addressed Stamped Envelope) containing at least 2 stamps to accommodate the extra postage for the playbill. The envelope should be at least 6x9 and you can fold it to fit into whatever size envelope you’re sending.
You can send both of those things for the cost of one postage stamp, and your package should be addressed to the Stage Manager, using the theater address as the recipient address:
(Example)
MEAN GIRLS
c/o Stage Manager
August Wilson Theatre
245 W 52nd Street
New York, NY 10019
Do NOT send them a blank playbill in this case. It will be discarded and replaced with an already prepared cast-signed playbill if they have them.
If you’re asking for just one cast member in particular, you do the same as above, but instead address it to the name of the cast member and not the Stage Manager. In this case, it is appropriate to include an unsigned playbill for them to sign (if that’s what you want).
"Mostly, I loved the size of these people's emotions. Nobody has emotions this size anymore. Outsized emotions. Operatic emotions. Kushemski and Vanda are like Tristan and Isolde, they're Paolo and Francesca. Nobody's in total thrall like this anymore. Nobody's overcome by passion like this, or goes through this kind of rage." Thomas, Venus in Fur