I want to highlight all instances of the plus sign in my document.
Open the Find and Replace window, Edit > Find and Replace (Ctrl+H).
In the Find field enter +. In the Replace field enter +.
Untick Regular Expressions
Click the *Format button, in the dialog select the Highlighting tab, select the colour highlight you want. Click OK.
Assuming you chose yellow, you should see immediately under the Replace field Yellow, Not Transparent. Click Replace All
This isn’t an ideal way to highlight characters; creating a character style would be better if you subsequently decided to change the effects. Cheers, Al
As an alternative, Find All (with Ctrl+H or Ctrl+F), then select the Highlight color (you can test multiple colors while text is selected).
If you work with Ctrl+H, don’t forget to…
Untick *Regular Expressions*
otherwise + has another meaning.