If HERO is tagged and if you interact with a mailbox, the prices of all the items will be discounted by 10% (only for hero)
For example, LIFE JAM would change from $300 CLAMS to $270 CLAMS if HERO is tagged.
Not only that, if you talk to certain people as HERO, you'll might get an item from them.

Another example, if you talk to SMOL as HERO, they'll give you a friendship bracelet.

I hope this helps! :)