My signature disappears every few days form my mac mail. why?

Try resetting the NVRAM. The NVRAM is a special memory section on your Mac that stores data that persists even when the Mac is shut off, such as volume settings and screen resolution - it's the information the computer uses to maintain settings after a reboot. You may have to do each of these several times because sometimes that's what it takes to stick.

Reset the NVRAM

How to Reset NVRAM / PRAM on your Mac - Apple Support

Reset the SMC

How to Reset the SMC of your Mac - Apple Support

Additionally, see if the problem can be fixed by starting in Safe mode (hold the shift key down at startup). It can take much longer to safe boot (10 min) so be patient.

How to use safe mode on your Mac - Apple Support 

Safe mode disables loading third-party drivers, forces the OS to do disk repair, clear certain caches and logs and other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's expected.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and re-evaluate the issue again.

If the problem is still unresolved, please return here and post a reply and we’ll see what else we can come up with for help.

njohnson924 wrote:

I have to recreate my signature in my Mac Mail at least once a week. It just disappears. Anyone know how to fix this?

Is this isolated to one single account..or all accounts?

From All Signatures you manually grab and drag the sig to the account you want to use it in.

In this example:

5 sig total, and drag & drop 4 to the account I want to see them in...

now you have options from the drop down in email:

Create and use email signatures in Mail on Mac - Apple Support