The image, which includes a background gradient shifting from yellow to black, uses the same font as the previous one which read "Dead No More." The assumption regarding Tuesday's teaser was that it was in reference to Wolverine, who is arguably Marvel's most high-profile dead character at the moment. The yellow and black color scheme could still reference Wolverine, who has notably worn variations of yellow and black throughout his forty year history. But the text, "Best Beware My Sting," doesn't make much sense for Wolverine.
The colors and the word sting could also reference the Wasp or Yellowjacket. The quote could be from the Shakespeare play "The Taming of the Shrew": "If I be waspish, best beware my sting." The quote and color scheme combined imply that this is a teaser for something involving the Wasp -- either Janet Van Dyne or another character that could take up the code name. But Janet Van Dyne herself is alive and will be seen in "All-New Wolverine" #5.
If both teasers are tied to the same character, and they need to be both dead and have a tie to Wasp or Yellowjacket, it's possible the character in question is Eric O'Grady. O'Grady was a previous Ant-Man who died in the pages of "Secret Avengers" in 2012. Could this be teasing his return as Yellowjacket or the Wasp?