Our theater just uses a paint pen on the upstage side of the baton itself.
With houseplot already up:
Draw two lines on the outside of the C-clamp
Then on the right side, write Instrument type (P=par, L=Leko, S=Strand, F=Fresnel)
Then the angle or size (19, 26, 36, 20, 40,50...)
Then the...