I've always thought it was sealing wax.
Interesting that this site below has it both ways!
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home.swipnet.se]
I don't know what ceiling wax might be but
sealing wax refers to when folks would send actual letters to each
other in an envelope. When you sealed the envelope,
you would put some hot sealing wax on the envelope flap
and then place stick your ring in the wax so folks would know it
was from you. If the seal was broken before the receiver opened the
envelope, they would know someone had tampeered with the note.
I guess this was an early attempt at protecting yourself from hackers ....
Gee, do I feel old now!!
Marv Peck
Y'all remember that rubber legged boy