My understanding is that tanks don't have locks or keys. The theory is that in an emergency you don't want your weapons neutralized while someone tries to remember where they left their keychain.

I can imagine a starship working this way. In fact, during The Neutral Zone Picard basically says as much:

RALPH: If they are so important, why don't they need an executive key?

PICARD: Aboard a starship, that is not necessary. We are all capable of exercising self-discipline. Now, you will refrain from using them.