A couple of things:

1. Penalty tries. If you award a PT, you must issue a Yellow Card. There are only two reasons for not issuing a YC:

• The act of foul play was not considered deliberate. To be honest, the list of ways in which that can arise is so short as to be almost negligible.
• You can’t identify the perpetrator. About the only example I can think of here is a maul heading to the goal line that gets collapsed and you can’t affirmatively ID the perp.

2. Yellow Cards – If given, they MUST be issued. If you are unclear on where things are to be reported, that information is available on this site.

If you have any questions, ask!