OpenStreetMap
It may sound strange but there are many shops which are dedicated to only selling watches & clocks. These shops also do repair works for them .
I searched for that tag in wiki . Looks like no one even proposed it ! There was one tag for public 'clock tower'
Diskussioun
Bemierkung vum daveemtb de(n) 15. Mäerz 2010 um 15:39 Auer
You can always make one up, and use it. I would suggest shop=clockmaker as per http://en.wikipedia.org/wiki/Clockmaker This is the typical term for this type of shop in British English, I can't vouch for other varieties. The rationale for "maker" in the name is in the wikipedia article - although most clocks and watches are now factory made, repairing antique clocks still requires the fabircating of components.
You could propose this on the wiki, I'm sure it would be fairly simple to get approved, but you never know!
Bemierkung vum pavithrans de(n) 15. Mäerz 2010 um 17:14 Auer
@daveemtb why not call it watch shop ? Because primarily there are more number of watches sold than clocks .
Bemierkung vum lyx de(n) 15. Mäerz 2010 um 21:02 Auer
Some people have already tagged such shops as shop=watchmaker. If you propose this on the wiki I guess it would be widely accepted.