My Dell Studio 1749 laptop doesn't have a visual indicator for caps or num lock. My solution ...
add the program indicator-keylock by entering the following command in a MATE terminal sudo apt install indicator-keylock enter your password when prompted - no text will be displayed as you type your password
add this program to your computer's start up by opening:
Control Center
Click Personal
Click Startup Applications
Click Add and you should then see ...
You may assign any name you wish
Command must be indicator-keylock
Click Add
The next startup will produce a visual indicator briefly on your screen when either caps or numlock is changed
Caps and Num locks are not only useful for devices without LED for state of keys, they are also very useful when remote desktop sharing ( Reminna, Teamviewer, DWservice and the likes ).
But then you need an indicator where you can change key-state by clicking - which LED indicators applet in Mate does not provide.
I don't know if Unity's indicators are still « usable » in Mate but this one did a very good job :
I managed to make it work in Ubuntu Budgie so it's worth the try in Mate ?