We are trying an image with a "Get out of your comfort zone" tagline. Using this on our agendas and social media footprints.
Sometimes we have members a bit reluctant to try a new role. In an effort to encourage them to try something new this appears on the agenda headers. This means it also appears in their inbox. Since the agendas have sign up links perhaps they will be brave and branch out.
This image and tagline also work in helping to recruit new members. The tagline details one of the core benefits of the TM experience. I added it on our Facebook and Google+ Plus pages.
We have the same image on our agendas, Facebook and Google+ Plus. This maintains a consistent club branding message.
I'm sure there are other images and phrases which both encourage existing members and also appeal to non-members. We'll see how this one works out.
Gmail Inbox (on laptop)
Facebook and Google+ Plus
Mobile phone (agenda)
The agenda image is 613 pixels wide which is wider than the mobile screen width in portrait orientation (fine in landscape orientation). However, most non-mobile email clients handle images 620 pixels wide or less just fine. So me mindful of your image width.