Hi Stephen,
Here you can find the origin and meaning of Hampe:
http://www.behindthename.com/messages/32964.html
You asked for more details (which I obviously didn't see last time), so I just had a look:
Other forms of the surname are Hempe, Hampel, Hempel, Hemprecht, Hampke, Hamke, Hempler, Hemprich, Hamp, Hemp, Hampo, Hampl etc.
(patronymic forms: Hempeler, Hempler, Hampler, Hampelmann, Hempelmann etc.)
The forms including an L are from the southern parts of the country.
The name Hampelmann is even the word for a "Jumping Jack" in Germany (as "hampeln" is a Low German expression for "struggle", "wriggle").
There is a German phrase: "Es sieht aus wie bei Hempels unterm Sofa" which means "It looks like under the couch of the Hempels' (family)" and is used when something is looking really untidy.
So Hempel and Hampelmann are quite funny surnames to have in Germany.
Regards, Satu