There is plenty – and varied – information available on using symbols in subject lines. Below Listrak Account Director Karen DiClemente shares some thoughts and best practices: 

When using symbols in subject lines, retailers are primarily trying to drive higher open rates. I encourage ALL clients to A/B test subject lines with and without symbols to see if the symbol actually made a significant impact on open rates.

Prior to using a symbol, here are a few questions I tell clients to ask themselves:

• How does using symbols in a subject line impact your brand (will they be seen as juvenile? Is this the brand impression you want your subscribers to have?)
• Does the content of the email warrant a symbol in the subject line?
• Make sure you are using symbols for a reason (not just to “use a symbol”):

1. Symbols can be used as a separator or punctuation
2. Symbols can be used to replace an actual word (ie. using a ? to replace the word “heart”)
3. Symbols can be used as a decorative design element

• Not all symbols render in all email clients – make sure you are using a rendering tool (ie. Email on Acid or Litmus) to ensure the symbol you chose will display correctly

The guide below provides some more detail: 

Subject Line Symbols by Email Client

Outlook 2010 – all symbols render correctly; color does not change

Outlook.com – all symbols render correctly; color changes based upon specific symbol

Comcast – all symbols render correctly; color does not change

Gmail – all symbols render correctly; color does not change

Yahoo – all symbols render correctly; color does not change

AOL/AIM – changes the 8th symbol; color does not change

Android – only the yellow symbols render correctly; color does not change

iOS (iPad/iPhone) – all symbols render correctly; color changes based upon specific symbol

Windows Phone – all symbols render correctly; color changes based upon specific symbol