Motion diagram. A Deaf-recorded clip from the PopSign corpus (CC BY 4.0) exists for this sign and can be placed here.
WHO
“who”
Hold a bent index finger just in front of your chin and flex it a couple of times, brows furrowed and lips slightly pursed.
A WH-question sign: hold furrowed brows across the whole question, and put WHO at the end — 'THAT WHO?'
Where the sign comes from
UnknownNo reliable source. We'd rather say so than invent one.
An older variant circles the index finger around the lips. Why the sign sits at the mouth is not established in any source we can cite, so we leave it unexplained rather than guess.
No sources — which is the point of the “unknown” tier. If you know of a documented account, the historical databases are where to check it.
The sign, taken apart
Every ASL sign is built from a handshape, a place it's made, and a movement. Learn to see these three and you can read and store any sign.
Made at the chin.
One-handed.
Repeated. Palm facing in.