You can find all filenames containing specific characters using ~= and “kind” as the search string.
~= is the special keyword that means “contains”
kind tells Windows wether you are looking for folders or files.
for example
kind:file filename:(~=”_”) would find all files with an underscore in their name
kind:file filename:(~=”(2)”) would find all files with a (2) in their name
kind:folder filename:(~=”ame”) will find all files and folders containing the phrase “ame”