If its a CA the signature should have been recognized when opening the applet.
check out the trace when opening and see it it's recognized.
http://forum.java.sun.com/thread.jspa?threadID=600033&tstart=60
look for the text:
You should inspect the full trace:
and
some significant pieces of information in there.
CA signed should use the default policy. If it's self signed provide a policy file and a keystore containing the signature:
http://forum.java.sun.com/thread.jspa?forumID=63&threadID=409341
look for the text:
This is the applet:
and
Solved