This information was found by Azzy. I don't know how many newsletters you need to sign up for but you can always remove yourself at a later date.
"If you're subscribed to our newsletters as of April 29, 2019, you will receive an exclusive Glowing Purple Mask skin.* Only available to subscribers, this in-game cosmetic item will give your Guild Wars 2 character mysterious, glowing purple eyes when applied to a piece of head armor." 
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