Edit: For clarity I am not talking about the spyglass spotting mechanic but the captain mark ability to identify targets to your crew.
Is the main purpose of captain mark to make to identify targets when the captain does not have a microphone and balance their dissadvantage against microphone users?
If yes, please make captain mark toggle between marked ships rather than click to mark.
Things that prevent you marking ships by targeting and clicking include:
Parts of the helm hull and baloon being in the way preventing a mark, a cloud blocking the click to mark but the target is nevertheless spotted, extreme difficulty in marking when in third person mode, difficulty marking targets at great distances, and the dissadvantage to have to target things while simultaneously flying the ship. (forcing to look at the enemy when there may be other things you are trying to navigate)
Another mechanic I would like to see would be an indicator for a marked ship to show on the map.
Edit: Crafeksterty has made a really interesting suggestion for additional captain mark abilities to show ally captains who you are targeting, and possible a mark that would tell an ally captain who to marc.