Support for special characters is good enough that they've become common in subject lines over the past 24 months or so, opening up many new creative opportunities. Sometimes special characters seem like they're used just for the sake of using them, just for the visual impact alone without any deeper strategy. But our 100 Inspiring Subject Lines includes some great examples of ones that have a higher purpose for their use of special characters:
This political group uses six black box characters to stand in for the word "censor," creating a powerful visual effect that simulates the act they're rallying against.
Using the circle-7 character in a subject line isn't all that interesting. But the really novel thing about this subject line is that Neiman Marcus brings that character into the design of the email. So when the email is opened, the circle-7 in the subject line emphasizes the one in the body of the email.
This is one of my four personal favorites. Until you can make your favicon or logo show up in the inbox, this execution by Jeep is the next best thing. Using bullet and vertical bar characters to approximate their logo is awesome. Talk about bringing brand impact to the inbox!
There have been subject lines in the past that used a similar checklist style, but they were forced to actually use the word "check." Now you don't have to. Vera Bradley's subject line is much tighter and much more natural by using the checkmark character.
Bullets, lists, and threes are powerful copywriting tactics. This subject line combines all of those into a succinct 1-2-3 list that explains exactly what you need to do to earn your free miles. The special number characters break up the subject line into small, functional chunks that makes it super easy to read and digest.
I hope these examples inspire you to look for your own opportunities to use special characters, and that 100 Inspiring Subject Lines gives many other ideas for effective subject lines.