Via US Credit Card Guide, increased signup bonuses are available for the following American Express cards through incognito windows/private browsing:
Amex Everyday, with 25,000 MR signup bonus:
Normally, the 25K signup bonus is only available through targeted offers. Now it’s available publicly for everyone! The required spend is increased to $2000 in the first 3 months.
The Everyday card has no annual fee, and allows full participation in the Membership Rewards program, making it a great place to park your Membership Rewards points if you need to cancel a Membership Rewards card with an annual fee.
The Amex Everyday card earns 2x MR points on supermarkets, and 1x everywhere else. If you use the card more than 20 times per billing period, you earn 20% extra points for that billing period.
Amex Blue Cash Everyday with $250 signup bonus:
As with the Everyday card, the increased signup bonus is usually only available through targeted offers. The required spend is only $1000 in the first 3 months. There’s no annual fee on the card.
With the Blue Cash Everyday, you earn 3% Cash Back at U.S. supermarkets, for up to $6,000 per year in purchases (then 1%), 2% Cash Back at U.S. gas stations, 2% Cash Back at select U.S. department stores, and 1% Cash Back on other purchases.