I sent a letter and SAE with US stamp to the stage manager on: 31st March 2014, and last Thursday I recieved this signed playbill back and note from the stage manager in a cardboard SAE which they paid postage on, mine wasn't returned, still really happy though.
address I used was:
Stage Manager of ' Shear Madness',
The Kennedy Centre,
2700 F St NW,
Washington
DC 20566
USA