Not sure if there is a need for that, :tr
should be able to do the job. Something like:
tr/ ?<>\\:*|"/_
but I hit unnoticed bug while testing it (thanks for that!), so the command should be like this in current version:
tr/ ?<>\\:*|"/__________
You can define a command:
command! sanitize :tr/ ?<>\\:*|"/__________