Unfortunately that only holds true on darker sigs. Try it on a light sig and you'll no doubt ruin it. Sometimes an overlay border works, as long as it doesn't have too much contrast. Then there's the option of no border, which does work more often than one may think (my latest is an example of this). However you've already stated that it's only for those that seem to be missing something, so that point isn't necessary. But that does bring up an important point; do not add a border just for the hell of it, rather only if it appears to be missing.