These can be as fancy or as simple as you like. There's no great mystery about them. Each gauge whether it be a dial caliper, a test indicator or a micrometer measuring standard needs to have a unique serial or ID number assigned to it. Most gages have these inscribed by the manufacturer. If you have a great many tools in your arsenal then you might want to create your own set of ID numbers to help you track them down. Scratch the numbers into the tool or use a permanent marker.
Avoid electro-engraving any tool with internal gears. The sparks from the process can cause tiny pinions to weld together. Don't electro-engrave anything with electronic components like digital calipers.
You'll want to set up a calibration sheet for each of these instruments. This sheet features the ID number for quick identification and its location in your shop. On the sheet you'll write down when the gage was calibrated and by whom, and when the next calibration is due. Then you'll attach the calibration certificate and keep them all in a binder, in a safe place.
If you send the gages out for calibration, you'll receive a certificate. If you calibrate these yourself, then you'll create your own certificate. On the certificate you'll note the instrument's ID number, a brief description of the tool and its graduations and range. Then you'll write down the test data which you obtained during calibration. Make note of the equipment which you used to make this calibration. It might be a gage block set, for instance. Date and initial, and you're done.
If you have many instruments to keep track of, then you'll probably want some software designed to automate this process, but we're more concerned with the small scale do-it-yourself approach here. We'll leave the software to someone else.
Now comes the label. This little sticker fits onto most tools and you'll simply write the tool's ID number on it, the date you had it calibrated and the date for the next calibration. Labels are often initialed by the person performing the calibration. If the sticker doesn't fit on the tool, or if the labels tend to peel off because of coolants or oils, then put the label on the tool's box. When you do that, make sure that an ID number on the instrument is linked to the ID number on the label and always put the gage back in its proper case, otherwise you'll mess things up.
And where do you get these labels? You could use pieces of masking tape, or an address label cut down to size and simply pen the information onto it. You could invest in fancy label printers that make really impressive calibration stickers with very, very tiny print.
Otherwise, preprinted labels make it quick and easy and they'll give your tool room a uniform, professional look. These vinyl labels are 1" by 1/2" and will fit most any tool.
PS: Interapid indicators have angular bodies so you'll have to trim the label to fit, or put it on the box. On Last Word indicators you could wrap the label around the body or, again, put it on the box. All you'll need is a ball point pen and you're set. Hint: if you keep the unused labels in the same loose-leaf binder as your calibration certificates, then you won't have to hunt for them next time. Many people put a piece of clear tape over the label to protect it. It's not a bad idea.