Thank you for your post.
I am unable to replicate the issue. Here is what I have done:
1. In FileMaker Pro 12.0v5 under Mac OS X 10.9.5, I created a database file with a Container field named "Signature".
2. I turned on Network Sharing.
3. In FileMaker Go 13.0v8, I accessed the file, added a record, tapped into the Signature field, tapped "Signature", entered a signature, tapped "Accept", and the signature appears on the device and in the record on the Mac.
Let me know what I am doing differently than you so I can replicate the issue.
I did the same thing, except I'm hosting the data base on a yosemite server, should i try with a regular Mac OS 10.9?
Your post shows Mac OS X 10.9. That is why I tested it under that system.
I have just hosted the file with FileMaker Pro 12.0v5 under Mac OS X 10.10.1, and following the same steps from my previous posting, I still get the same results. I also tested (successfully) with FileMaker Pro 13.0v4 under Mac OS X 10.10.1.