What is the ruling on remaining silent regarding advising women about using perfume in public, knowing that the silence might be due to shyness or fear of a reaction?

It is obligatory to condemn evil according to one's ability, and this obligation is not waived by the mere apprehension of a reproof or rebuke from a transgressor. The means of condemnation are numerous. One could, for example, write the ruling on a woman's use of perfume and hang it in a visible place.