Bergmann bayard
 

Just aquired a BERGMANN BAYARD (S#17700) and unit #4604. Bought on line and hope someone can tell me something about it as I know nothing about it - When/where it was made, seen service?

Nice catch! It's an early issue Danish 1910/21. Denmark adopted the Bergmann-Bayard in 1910 and revised it in 1921, hence the 1910/21 designation. Pieper only made these until WWI broke out, so your gun must have been made between 1910 and 1914. If you look at the right side of the frame right above the grip, you'll probably find an inventory number.

Edit: I just saw that you found the number "4604", this is the inventory number. I could very well be wrong, but I don't think these were ever unit marked.

The S# is 17700 and 4604 would be the weapon number for whatever unit it was assigned to.