Try running this in Terminal (/Applications/Utilities/Terminal.app):
mdfind "kMDItemContentType == 'com.apple.application-bundle'" -onlyin $scope
# $scope is your search range
# this command will only search all the applications under the given scope if -onlyin is specified
This is a search query that searches items with the given metadata predicate ...
I was able to do it by using a rectangular annotation via Tools -> Annotate -> Rectangle. Make sure it covers the signature and just make the background and border match the color of your document background (white in my case).
This is a variant built off of the answer from @Lri. It will stay silent if there are no processes above a threshold (set to 60 here) but does not do averaging across samples, so may give more one-off noise. Like the other answer, you will need to install terminal-notifier.
Save the script below to a file (called, e.g., /Users/goldberg/cpu_notify and made ...