Mark – In Magic – the most basic type of creation. As a personal mark – a signature, sigil or glyph. Used for self identity – marking a spot for various purposes, tagging (with graffiti for example), etc. Mark places of significance.
Magic Portal – Portal is a more complex creation than a mark. It's purpose is either to reach (transfer to) another place in space and time or state. Portals can be used for teleportation or summoning.
These are some examples. I unexpectedly found Brighid cross in a circle and included it here. From left to right top to bottom: Ouroboros, Brighid cross, Brighid cross in a circle, Pentagram, Tao, Sun wheel, Chaos. There are many other possibilities on constructing or symbolizing a portal. It does not have to be one of these symbols and it does not need to be contained in a circle. It can be any number of shapes, for example square, rectangle, triangle, arbitrary shape, cross, anything one can go through.
One idea with Magic Portals is that the same types of Portals are connected with each other. For example, you if you have a Pentagram portal (very common symbol), you can travel to any other Pentagram in the world. Same is true for other portals.
Other symbols of interest: Latin cross, Infinity triangle, Raelian star, Infinity, Ichthys wheel.
These are all Symbols, but a Portal is not just a symbol. It is a method of transfer. One theoretically goes through the portal. So it's like a door, except that you can change where it leads to.
Some pictures of portals for inspiration.
