@NeoAc: Kindrid spirits man. It works for e-mails, everything! Blows my mind really.
@axle19: If said person is like me, they could have simply read it to acknowledge their acceptance and understanding of the PM. That is if they know about the bold PM thing. If they don't know, they could have just read it and decided to reply later. I did that a lot at school. Unfortunately, I forgot about the PM due to the lack of flashing red. Maybe you should shoot a reminder PM after a few more days. If you can't wait that long, do it now!