If the transaction is scheduled to earn bonus points an icon will appear next to it shortly after it posts to your account (not while still Pending). These icons are not completely reliable. Once the statement is generated the icons vanish. A month later, after the points post from pending, you will be able to find a definitive list of transactions that earned a bonus on membershiprewards.com > Points Summary > Activity Detail > Click [+] > See Card Bonus Detail.
This is actually the opposite of how it appears for me. I don't see any 4x icons on my recent activity page, but once my statement closes, I do see the 4x icons on my Current Statement view.