

(Why are there
signs)
Good question, here’s the explanation man sudoers
offers:
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user-IDs
(prefixed with ‘#’), system group names and IDs (prefixed with ‘%’
and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-Unix
group names and IDs (prefixed with ‘%:’ and ‘%:#’ respectively),
and User_Aliases. Each list item may be prefixed with zero or more
‘!’ operators. An odd number of ‘!’ operators negate the value of
the item; an even number just cancel each other out. User
netgroups are matched using the user and domain members only; the
host member is not used when matching.
TL;DR lets the system know the following word is a group name, instead of a username
No problem, I love when people show curiosity, and I’m happy to help where I can