/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/bin/jarsigner is in gcj-4.8-jdk 4.8.5-4ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/bin/../../../../bin/gjarsigner-4.8