About thirty years ago I would write to famous musicians, composure and actors to ask for an autograph on a First Day Cover.
I would choose a FDC that had a theme associated with the celebrity.
This FDC is from a friend's collection that I bought in the late 1980s
Hazel is a classic strip and here is a very nice example of a signed sketch.
GUARANTEED AUTHENTIC FOR LIFE
Ships the next day in a padded envelop between cardboard with delivery confirmation.