blue checkmark

A  blue checkmark  is used on some sites to indicate a verified user account, and other sites as an indicator that the user paid a one time or subscription fee.

Twitter
Twitter used to (before November 2022) use a blue checkmark to indicate a verified profile.

Since November 2022, Twitter added an option to their Twitter Blue premium subscription offering to display a blue checkmark next to your profile

Tumblr
As a joke, Tumblr started to offer two blue checkmarks next to your name for a one-time fee of $7.99 (the same as the monthly fee for Twitter Blue).


 * https://twitter.com/photomatt/status/1590796122821623808
 * "A checkmark isn't cool, you know what's cool? Two checkmarks. https://www.tumblr.com/staff/700564142648606720/hi-were-introducing-completely-useless-blue" @photomatt November 10, 2022

Tumblr allows purchasing multiple pairs of blue checkmarks and they stack up next to your name:
 * https://twitter.com/photomatt/status/1590798662669832192
 * "How much would you like to pay? You can buy the upgrade multiple times and it will continue adding more checkmarks to your profile. ✔✔✔✔" @photomatt November 10, 2022
 * An example of a post from a profile with 8 checkmarks: https://www.tumblr.com/raz/700565373239672832/do-devs-get-8-checkmarks-by-default-or-did-you-buy