How about using one of these gadgets mentioned in this excellent blog post to remind you :
and with every notification you can ask yourself whether you were mindful? If yes then tick 1 on the beeminder goal. For a starter it's enough (even too good) if your goal is 1 times/day you were mindful.
The other pro of this method is that it will correct your state and bring you back to mindfulness (the blog post was originally intended to that purpose only) which is an important training to your goal and serves to help you to track it too, like you wished.
This idea was lurking in my mind for years and never tried to buy such thing. Now you kindled my interest again and most likely I will do what I suggested for you. For the past, I was trying to depend on the hourly beep of my digital watch but mostly got unnoticed. So it seems, buying a fitbit or a bracelet is the way to go for me.