I believe it is a reference to the last payment, so the minus will be displayed until you reach the payment threshold. So as Ravinder said, it is nothing to worry about.
One of the fresh Adsense accounts I manage, that hasn’t made a payout yet, doesn’t show the minus next to the earnings, yet another account I look after that has had a payout, does show it.
So they are either A/B testing a new feature, or it only applies to Adsense accounts that have previously paid out.
FYI, I’m sure you’re violating Google Adsense policy by showing us your Page RPM, so I recommend removing that image to be safe.
Here’s what you can and can’t say. Source: Google Groups
“you can not tell people about specifics like the amount of click through rate (CTR), earnings per click, EPC, RPM, etc.
You can tell others what the total amount Google paid to you is..
So you can say “In Dec I made $xxx from Google AdSense”
You cannot say “My clickthrough rate for December was 5.3%”
You cannot say “My donkey grooming site earns $252.38 per click from adsense”
This one’s tricky, you can’t say “In December I made $2,238 from 581 adsense clicks” Because while it’s ok to say you’re gross payments providing how many clicks you had is not appropriate and allows people to derive your EPC.
I believe you can say things like “Holy Toledo! My CTR doubled when I changed the colors of my AdSense ads” because you’re not giving specifics about the performance of the ads, just about the performance of your optimizations. You can’t say ‘My CTR went from 100% to 200% though’.”