Hello friends!
I read a few days back that they were supposed to 'bump up' the new account bonus on the Amazon Store Card for 'Prime Day', but I've now confirmed on the website that the bonus for new applications that are approved today for the Amazon Store Card (Synchrony) is a $50 Amazon Gift card for Amazon Prime members.
I'm sharing this so that anybody who was planning on applying anyway in the near future will know that it might make sense to apply today, depending on what your 'usual' bonus offer is (most of the year my own is usually $20 for the store card).
Note that this is the Amazon Store Card, not the Amazon Chase Visa card. Oddly, my own bonus for the Visa card is the same as it always is, so there is no special reason/urgency to consider it today. 
Also note that the $50 bonus offer only applies to Amazon Prime members... I'm not sure if a trial membership would work to trigger the $50 bonus, but it's worth a try! (It will tell you up front once you're logged in).
@Anonymous wrote:
Thanks! I saw a $50 offer yesterday too and swore it was the store card (this girl needs some new workout equipment).......
I'll check later today. I've been holding off pulling the trigger, I'm gardening 8 days strong but $50 bucks is a good chunk of change on my $129 cart of stuff - oh the drama of thinking of stepping out of the garden AGAIN. The worst part is, it forces me back to the desktop to fix my signature, that's just rough!
Ah, they started it early! I missed that... sorry! 
In any case it's (still) up now, and from what I can tell it will be going through the end of the day, which if it's on "Amazon Time" will mean until midnight PDT. 
(If I were genuinely interested, though, I'm not sure I would test this hypothesis and wait until the last moment, although Amazon would likely make it good in any case.)