I have a number of keys on my keyring - screen door, main door, garage door, some random key that I don't know where it goes, etc. When I purchased the house, the previous owner placed different coloured zip ties on each key for identification and snipped the tails off. This is pretty clever but adds to the bulk of the keyring. What is another good way to identify the keys? The heads are assorted shapes and sizes.
Since I have lots of different color permanent markers, but not lots of different colors of nail polish, I use my wife's clear nail polish.
Mark the key up with the sharpie - I usually put a dot on - and then a drop of clear nail polish to cover it and keep it on there. Once dry, it stays on there forever - or until you use nail polish remover to remove it.
I have added notches to the side of the key head in the past. One of the advantages to using this method is that you can find the correct key in the dark.
Start with this:
Take a file to the edge of the key head. Move it back and forth to create a furrow. End up with this:
Add as many notches to the key as you require. If your key has a flat edge that isn't used by the pins to unlock the lock, you can also use that side.
Coloring the keys is a good way to go.
For coloring I would suggest nail polish, which is quite durable. Other spray paint might be tried as well, but nail polish is really accessible and easy to apply.
If you want you could even mark keys with letters or numbers or symbols. But please take care not inviting thieves by writing house number or address on the keys. Make the markings subtle and the meaning known only to you and those using the keys.
You could try to group them together in small clusters based on your daily activity, and even put them in a sequence based on step by step usage. Add a label rather than a color on each key, especially if you have a lot. If the keys keep adding, an idea would be to switch "technology" (badge-based access systems etc.).
1/4" Professional 36pc Letter & Number Stamp Punch Set
I use order and memory.
Start by removing any keys you don't need on your keyring. They're just adding to the bulk from the off.
I order my keys by frequency of use and by direction where one way represents locks at the front of my house and the other way represents locks at the back of my house. The car key is the "root", the key next to this is "forwards".
While this exact pattern might not work for you, I'm sure you could come up with something similar to suit. If you need a lot of keys, I'd consider two keyrings linked together with i.e. one for work and one for home, or one for inside and one for outside.
Since nobody has mentioned it: Split it up into multiple rings. E.g. you can put your work keys on one ring, your home keys on another, and the car keys on a third, then link all the rings together. This has the advantage that if you need to separate them for any reason (say, to give your car keys to the repair shop, or lend your home keys to the neighbor when you go on vacation so they can water your plants), it's as simple as separating that one ring.
There are a lot of key organizing product on market. I use a Keysmart organizer to organize all my keys into a slim case. Other brands of similar products are available too if you just do a simple google search for key organizers.
As to identify the keys, usually I arrange them in the order of most frequently used, but I think with this type of organizer, you can also use permanent marker or nail polish to color code back side/the spine part of the keys as labels.
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Discard this idea if you're looking for quick identification with the requirement of some memorization (i.e. colors).
Personally, I use a metal engraver from Amazon (roughly $14) and write something on the key. I use an acronym (SR = Snowboard Rack) or a name/word (Dad = Dad's house). The benefit of this is that you can be descriptive, but the downside is that you will need to take a close look at your keys.