I have a number of bikes. I have found a certain type of bike lock to be optimal. Thus, I have no less than four keys of similar type. The lock manufacturing company changed the design of the key at some point of time, so two of the old keys have an identical base and two of the new keys have an identical base.
When needing to lock or unlock a given bike, I can distinguish between the old and new key base type, so that leaves me two keys to choose from. If I blindly use a key, 50% of the time I guess incorrectly.
Is there some way I can easily and durably mark the keys so that I can distinguish them from each other?