Adding brackets to a subject line

[SOMarketing]

I'm attempting to use brackets [] in my subject line, similar to: [Members] This Week's Announcements However, I'm unable to save this subject line because the tool thinks I'm trying to add a personalization. I get the red error "Make sure you are not missing a part of your subject line personalization." and I'm unable to save my email settings. Is there a way to character escape those brackets so that I can use them as part of my subject line?

[William_A]

Hello @SOMarketing ,

I'd recommend using something other than brackets for the purpose of the subject line in this instance. Either (Members), or include a bit about this being exclusive for members in the preheader line to show after the subject.