I’m curious,
anyone has any idea why is it there and what is it for???
It looked like a tribal tattoo to me, probably something Sally had done when she was younger and living the city life. I don’t know if there was any real symbolism behind it, other than her thinking that it just looked pretty cool. 
Well, I have a fanfiction where she mentions she was “young and stupid” so I was thinking maybe a collage spring break or something, back in her wilder days. I guess I got that idea from a song that goes:
She’s got an MBA and a plush corner office
She’s got a don’t mess with me attitude
She’ll close a deal she don’t reveal that she can feel
The loneliness the emptiness
Except when she comes in here
She’s the product of the Me generation
She’s got a rock and roll side when you get her agitated
She got the tattoo there on her derriere from a spring break dare
In Panama where love was all she thought she’d ever need
HEY Rac_Rules! I didn’t know you were on here too… 
What song is that again?
Hey foreignconcepts! I remember you, you dropped that detailed review for my Cars/24 crossover fanfic on Fanfic.net! Thanks, and nice to meet you on PP!
LOL hey, foreignconcepts. Yep, I’m here too. The song is “H*** Yeah” by Montgomery Gentry. For some reason the music video has been flagged for 18 and older on Youtube, though I don’t know why the heck why.
Well her reaction to him seeing it was indicating how she was coming around on Lightning.
HAH, why would anyone flag a country video 18+? I’m sure it’s not Rascal Flatts’ I Melt (which I absolutely love them for making!).
I think Sally’s (unintentional?) spoiler flip-up was a show of self-consciousness. She realized that she kind of painted herself into a corner verbally with her offer of lodging for McQueen (“So I thought you’d like to stay with me… O_O I mean, not with me, etc…”) and her spoiler may have flipped up without her really realizing it, if that makes sense.