You can get more detailed information by using the verbose flag like this to increase the level of verbosity:
codesign --verify --verbose=4
codesign --verify -vvvv
codesign -v -vvvv
These are all the same command, just different ways of inputting it:
-v, --verbose Sets (with a numeric value) or increments the verbosity level of output. Without the verbose option, no output is produced upon success, in the classic UNIX style. If no other options request a different action, the first -v encountered will be interpreted as --verify instead (and does not increase verbosity).
Apple considers this a 'bug' according to their man page:
The dual meaning of the -v option, indicating either verbosity or verification, confuses some people. If you find it confusing, use the unambiguous long forms --verbose and --verify instead.
There are also some free utilities available such as Codesign Checker, that might be useful.