Stamp 1 cent G. Washington perf. 10 x 11 single watermark (?)

Stamp 1 cent G. Washington perf. 10 x 11 single watermark (?) Perforation: 10 horizontal and 11 vertical Face value: 1 cent Year: 1920 ? Green color Watermark: single S up on the right side (?) Used I am not aware of this postage stamp in the Stampworld and Colnect net catalogue. I can't find any information with this kind of stamp (I only know the 10 x 11 example without watermark from 1920) If there is anyone who can inform me about this postage stamp, I would appreciate it.