I guess - as witcher signs are mostly energy and elemental spells - there could be something similar, e.g.
- ground lash to whip enemy(ies) on medium distance
- wild "state" to increase animal instincts and combat attributes
- water bubbles;
but the way it is right now seems most lore fitting and "normal" to the world, as witchers are "magic noobs",
so the signs should be used only in some emergency situations.
As about witcher 4,
probably it would need to come years from now, open totally new story and everything,
and only keep most significant elements from witcher universe,
to make everything feel new, unexplored, interesting.
Or more like for it to come NOW - when there is still some audience, or never.
Maybe another Elemental Like one, we have Fire, and wind. Don;t know how Earth could work but Water could maybe work where once cast, the water Surrounds the opponents Face. In affect Drowning them or causing them to submit maybe? Great against fire based opponents and air breathing targets, Pointless against aquatic creatures like Drowners?
just an idea though of course.