@RainbowDash69  
The artist will be turning these into keychains, I believe. So they are individual images.

i would say there are too many signatures  
really can’t one just do at the bottom (make it really big?)

@Minus  
I don’t really agree. I don’t dislike any of them (not even Bon Bon any more; she became much more likeable this season). But this isn’t who I would rate as the six best or even six most loved. This grouping seems defined more by the fanon ships than the actual popularity of the individual characters. Derpy, unquestionably, is #1, and Lyra is probably the second most popular background pony. Vinyl Scratch is probably #3, assuming she’s not actually ahead of Lyra right at the moment due to the bump she got from actually appearing in the last episode. But whoever’s #2 and whoever’s #3, those are the top three. No question they’re in the Background Six.
 
But why is Bon Bon there? Does anyone really like her more than Berry Punch or Colgate. Fourth most common, maybe, but it’s entirely because she’s paired with Lyra, not because she herself has much actual appeal outside of the fanon relationship. Octavia is cute, and like Vinyl has a unique appearance, but she’s had a measly two episodes where she’s so much as appeared. Not even one per season. If she never appeared again in the show it wouldn’t really affect the show, or even be noticed by most viewers. Is she there for any reason other than that she’s fan-shipped with Vinyl a lot? With Dr. Whooves, if you take away the images where he’s paired with Derpy, his number of images drops by half – below that of Berry Punch. And that for a character whose appeal rests largely on being an accidental pop culture reference to an entirely different character. He‘s not that popular; Derpy and Dr. Who are.
 
I think if you look at the ponies for themselves rather than to complete the half-sets defined by the first three, Berry Punch would probably be #4 and Colgate #5 most popular, not #7 and #8. Cloudchaser might be #6, but I’m not really sure I’m judging her popularity accurately. I’m hardly unbiased. (I’m not unbiased regarding Lyra either, but I think objectively, it’s not bias that leads to rating her as #2. Even TVTropes.com says she’s #2 after Derpy.)

@Ferrotter  
There isn’t though. These are THE 6 that we all know and love. Berry Punch and Colgate would be the next pair in line, probably. But however many you add it’s always gonna be earth pony dominated. Seems to just be an unwritten rule of PG ponies.  
That’s hardly a bad thing though. It doesn’t make them less deserving.

Too many Earth ponies, not enough Pegasi or Alicorns. The trouble with a Background Six is there are more than six deserving.