Etymology of BSL : 100 hundred, 1000 thousand

100

http://bslsignbank.ucl.ac.uk/dictionary/words/hundred-1.html

Finger pointing horizontally under chin

The fist and curled fingers under chin moving horizontally represent the two 0’s of 100.

Note, some signers have a very relaxed hand making the shape less obvious.

1000

http://bslsignbank.ucl.ac.uk/dictionary/words/thousand-2.html

Index finger carving a short arc in the air.

The short arc represents the comma when used to write 1000 in a formal way ie 1,000