How about, 'type you name here' and it spits out paper tape with it
punched as text? (I have C code for this). Paper tape is cheap even
today, as you'd only need a foot or two per visitor.
(And if the tape had their name also coded as machine-readable, you
could use it as a 'ticket' for other displays or activities...)
Cards would work, but are more cumbersome to make just one, and tape
readers can be nice and little and non-threatening (and harder to harm).