Not sure what you mean by a "digital font", but we have several clients who have AP checks with signatures embedded in the Crystal check form. Of course, they need to be careful with their security settings. Your Sage Reseller should be able to assist you with this.

Indeed. 

We've done this using an embedded image with suppression logic (based on the PrintedByUser)... or with a formula to swap in a user specific image (again based on PrintedByUser).

Are you using the Troy driver to provide the digital signature or are you trying to create the signature within Crystal Reports? Troy has multiple levels of security built into its devices and drivers. They have a process to do the digital signature. The problem is that Troy and the Crystal runtime with .net doesn't really work well. Running it in designer works but not through the runtime. It can be tricky getting some of the security features working, if you can. 

If you need security and you don't want to use a check signing machine cause you can't use the Troy functions for check signing, then you can still set this up in Sage with a little work. High level overview you would create a UDF with the path to the image of the signature (not the digital signature Troy created for use with their system). This path should be to a USB drive that is setup to always connect as a specific Drive Letter. You can also get a drive that requires a pin before it is available for use. This would mean for security the user would have to have the USB on their machine and have a Pin entered to sign checks. Then in crystal use image of ***VOID*** as the default signature and change the graphic location to the UDF containing the path of the signature. This would default to image of ***void*** if you do not have the USB drive available.