It all depends on where the message occurs. If the message is next to their address then it means little because that is just the "Full Name" setting in a chat programme. Some chatters just put that there it make the 'whoisers' out there wonder about it all.
If the message was in a private or notice reply then the user you whois'd is likely to be an oper as they are the only ones that can tell when you do a whois on them. They get the message via a server notice and could script an automated reply via that.
With only 10 characters to play with? Better off editing Full Name setting. Though, of course, that will not actually count the number of whoises you get. Only an oper would be able to have that privilege.