Like I also replied to you on Twitter; these are just previews and not representative of the final game. Any stats are just placeholders at the moment too, the picture is mainly to showcase the different classes discussed in the update.

The class icons are in the circles next to the Health bars, and the Tank one you were looking for is indeed the Shield like you suggested after. Healer is the '+' icon, a common sign for First Aid, Medics or for example the World of Warcraft Healer icon if we are staying within the RPG scene.
We don't want to be excessively creative with this; we want to use symbols that are commonly used in both real life and gaming so people instantly recognise them.

Our main aim at this moment in time is to create a playable beta version of the new RPG-style game for our community to test, which means small cosmetic changes are quite far down the priority list. We'll take your feedback into account for future reference though, and combined with/depending on other community feedback we receive we may or may not make certain changes.