Feature: When holding a Tardis key, you can shift click (not on ground just in front of you) to activate a beacon from your Tardis' light thing on top that only the owner of that Tardis can see. But the beacon is not like a vanilla Minecraft beacon, It will be like a translucent beacon that you can see through all blocks except bedrock. (as for why someone would have bedrock blocking there Tardis, I haven't the faintest idea.) and to toggle it on and off of course you would simple shift click an empty space.

Any More 'bright' ideas?: No i think that is it for now. Thank you for your time.

Or an alternative is while holding the key, you can simply press a key on your keyboard (default b) to toggle it on and off.