Can You Lift Signatures Off A Chalkboard?

I was watching old shows of “What’s My Line”

Here’s Liz Taylor’s (for example)

When the celebrity guests come on, they sign in on a chalk board. I was thinking that if you could somehow have saved all those signatures how much it’d be worth.

Then I got to thinking, is there anyway to lift a signature or any other writing off a chalkboard? I mean if they are using it as in “What’s My Line”

Sure, just use tape.
The same way police dust for fingerprints.

Slab of clay.