I have lots of sMerit. But, how do I know if I am a merit source or not?
You probably aren't. AFAIK theymos sent a PM to every user who was choosen to become a merit source.
But you can check in the merit page:
https://bitcointalk.org/index.php?action=meritYou should see something like this if you are a merit source:
For me (and other sources), it is. My merit page reads
"You are a merit source. The next XXX merit you spend will come from your source rather than your sMerit balance. Merit spent from your source will come back in 30 days. Unused source merit is wasted. It is not allowed for merit sources to sell their merit."