Mark Occurrences button missing

I've used this feature and it really can be a great aid. Today I have a
excellent example of a situation where it would help, but the button is
missing on my toolbar. I'm sure it's because I've customized the toolbar
in my perspective to eliminate a lot of irrelevant stuff, but I
accidentally eliminated the highlighter. Switching back to the standard
Remote Systems Explorer perspective does bring it back, but I really would
like to add it back to my custom perspective.

Can anyone direct me to what would be necessary to show it? I've not had a
great experience with the 'Customize Perspective' option showing me what
is and isn't really active.

Thanks