lock, latch, stamp, seal
鈐 centers on a metal device used for securing or authenticating: a lock or latch for fastening, and a stamp or seal for marking ownership or authority.
鈐 combines 金 (metal) with 今, which likely contributes the sound. The character originally referred to a metal lock or seal.
Metal 金 plus 今 (now) suggests a metal device that secures things in the present moment: a lock that keeps things shut now, or a stamp that marks the current moment of approval.
For ケン, imagine a metal lock shaped like the letter K, and you need a key to open it: K -> ケン, and the lock is made of metal.