Do not risk getting cards, or irritating referees, for no good reason.
During the finals of the Men´s Sabre Team event of 2007 World Championships, this happened:
Go to 31:24, in the penultimate bout between Aron Szilagyi (On the left) and Boris Sanson on the right). As you see, Sanson shows off with an extended finger when celebrating a scored point. At first sight, I thought it was his middle finger, and it was only during reviewing the footage again that I saw that it was the index finger that Sanson extended. At this level, the referees have video replay to check up such things, but the overwhelming majority of fencing matches are fought without VR.
Lesson for young fencers: Even if the referee got it right at the first viewing- or did not observe the finger at all – there is no guarantee that your referee at a lower level match will do that. When you start the match, the referee will in the overwhelming majority of cases attempt to be impartial, and will not look out for faults committed by one fencer more than the other. Both you and your opponent have a modicum of goodwill in the eyes of the referee. This goodwill is a resource to value, and it is – in contrast to most other resources – a resource that you do not have to do anything special to maintain. You just have to avoid frittering it away by testing the patience of the referee. In order to avoid just that, you should not try your luck with anything similar.
Put shorter: Never risk irritating people for no good reason!