@Jay_Wackal  
Really ? Very nice, welcome ! :D
 
For the canon ponies you can look at the MLP Vector Club’s color guide where they show the direction of the CM, usually the pony facing right (it’s always mentioned which direction they’re facing if for some reason the pic doesn’t make it apparent). Case in point: Rainbow Dash.
 
For OC’s you need to infer from refs or otherwise 1st appearance of the char with a CM cuz I’ve seen that mentioned only once or twice.

@StormsparkPegasus  
I’ll remember this next time I draw them. I only just got into the whole mlp thing last year so there’s still a lot for me to learn. Thank you though ^-

Take this as constructive criticism…on each side, the CM is mirrored compared to the other side. The end result is, if you look at them from above, looking down at their back, no matter what the CM is, seeing both sides together like that will always be symmetrical. I’m pretty terrible at explaining. On Dashie’s CM, the red part always faces her front. I guess in this case your reference was wrong, haha. To be fair, CM errors aren’t unknown in the show itself…I can’t recall a time when Dashie’s was ever backwards, but there have been occasions where others were.

@Jay_Wackal  
You can flip it …

@StormsparkPegasus  
Plus this was my ref
 
https://i.pinimg.com/originals/76/2d/99/762d998dc47bee07e4a124c916401e6a.png

@StormsparkPegasus  
I got the cutie mark from google lol

It’s good art, but why do so many artists get Dashie’s cutie mark backwards?