Ignore messages on Messenger mutes someone’s messages and add them to message request folder without them even noticing that you did it.
Now the answer to the question of whether your Messenger contacts will notice that you have just moved them to ignored list (message request) is NO.
Messenger does ignore message in such a way that nobody knows whether their messages have been ignored or not.
The only suspicion from someone you moved to message request is that their messages will just be sent without being delivered.
To some people that care, they will definitely be worried why their messages are not delivered.