If X puts Y on ignore, the only way Y is going to know is if Y tries to PM X and if they're not "friends" that's not likely to happen? I only PM with friends so I wouldn't know if I were on ignore by someone else. There's no way to know that someone isn't reading your posts or anything. It's not meant to be intrusive or a "punishment" to the person being ignored or anything like that but a help to the person who needs to ignore another person for awhile to feel better/safer. It doesn't really/isn't meant to affect the person being ignored I don't think.