How do I fix the missing memory stick symbol on Mac after unplugging without ejecting?

Assuming you have plugged the stick back in and it's not showing up in Finder, it may have been corrupted by removing it without ejecting it.

Open the Disk Utility app and see if the stick appears there, select it, and click on First Aid and follow the prompts.

click here ➜ How to repair a Mac storage device with Disk Utility - Apple Support

MettamB wrote:

I have removed a memory stick without ejecting it first and now my MacBook won't display the memory stick symbol on my home screen, what can I do please

It might be corrupted. Open the Disk Utility app, select it (it should still appear in Disk Utility even if it's not showing up in the Finder or on the Desktop) and click 'First Aid' at the top, then let it scan.

Then it's not getting mounted at all.

Which means it likely failed entirely.

Your only option is to try to plug it in to another computer and see if it shows up. If it doesn't, then it's almost certainly a hardware failure.