Skateboard Sparks happen when you are grinding and a spark flies off the trucks. It's rare. I have seen in 4 or five times in 20 years of skateboarding.
Grinds are loud and rough and when they spark it is pretty sick. Not much will make you feel more gnarly then making fire from your grind.
They had an option in Tony Hawk Pro Skater to have either flames or sparks come off the trucks when in a grind.
You can buy sparkers to put on your trucks and tail of your deck. They have flint on them to make a lot of sparks. It looks pretty gnar when a hail of sparks fly off you board when skating.
So if you wanna be a sparker you can grind until your heart is content. You can even start a fire too...be careful...