How to see/check a signed gem without installation?

[nobu]

Describe the problem as clearly as you can

I'd like to see/check a signed gem without installation, but could not find how to do it.

gem cert manages certificates themselves only, does not seem for gem files.
No other related command found in gem help commands.

Did you try upgrading RubyGems?

Using ruby/ruby@72b8fa9e03f.