There is no straight forward out of the box framework support to add an signature image to a Crystal Report. 

However IFS Report Designer layouts does have the support to add a signature to the generated PDF report. This is for Operational Reports.

Actually you can try to add your signature as a media object to somewhere in IFS and get it into your crystal report with a query.

For example we are using it in our shop order report (which we designed in crystal reports). We have media items added on Routing Head and we have a query as below to get them into our shop order report.

In crystal it is a subreport with a graphic object.

I hope it can be helpful.