“What do snowmen wear on their heads?”/“Ice caps.”

A popular winter riddle is:
 
Q: What do snowmen wear on their heads?
A: Ice caps.
 
The joke has been cited in print since at least 1994.
 
   
Google Books
The Father Christmas:
It’s a Blooming Terrible Joke Book
By Raymond Briggs
London: Puffin Books
1994
Pg. 54:
What do snowmen wear on their heads?
Ice caps
 
Google Groups: alt.humor.puns
Puns of the Weak 12/13/02
Stan Kegel
12/13/02
(...)
What do snowmen wear on their heads?
Ice caps ! (Kids Jokes)
 
Google Groups: alt.tv.lost
OT: snowman jokes
AirDuct-Kate
9/28/05
(...)
What do snowmen wear on their heads ?
Ice caps !
 
Google Books
On Thin Ice
By Nancy E. Krulik
New Yok, NY: Grosset & Dunlap
2007
Pg. 109:
“What do snowmen wear on their heads?” he read.
 
“Ice caps!” Andy replied, holding up his snowflake.
 
Twitter
Mickie Rops
‏@mickierops
Another one for @santaclaus25 What do snowmen wear on their heads?...........ice caps, of course.
11:46 AM - 12 Aug 2008
 
Google Books
Christmas Crackers
By Matt Wilce
Lulu Publishing (Lulu.com)
2012
Pg. ?:
What do snowmen wear on their heads?
Ice caps!
 
Google Books
Christmas Jokes and Riddles for Kids
By Christy Davis
Published by author
2013
Pg. ?:
What do snowmen wear on their heads?
Ice Caps
 
Google Books
Gigglers: Christmas Jokes
By Toby Reynolds
London: Scholastic Fiction
2015
Pg. 71:
Q. What do snowmen wear on their heads?
A. Ice caps!
   
Mirror (UK)
The top 30 Christmas cracker jokes of 2016 revealed - and they’re actually funny
30 new cracker jokes for this Christmas have been compiled following a competition to find the best wisecracks to entertain the family
BYRUKI SAYID, LAURA CONNOR
09:13, 22 DEC 2016 UPDATED 09:14, 22 DEC 2016
(...)
What do snowmen wear on their heads? Ice caps.