General Descriptors:
* Permanent
* Waterproof
* Dry-erase
* Sharpie (as a brand name)
* Colored
* Black
* Red (or any other specific color)
* Bold
* Fine-point
* Broad-tip
* Retractable
* Washable
* Non-toxic
* Highlighter
* Whiteboard
* Chalk
* Sticky (referring to sticky notes)
* Faded
* Used
* New
More Descriptive Adjectives:
* Vibrant
* Luminous
* Opaque
* Transparent
* Smudgy
* Sharp
* Fuzzy
* Thick
* Thin
* Sturdy
* Flimsy
* Colorful
* Brilliant
* Dull
* Heavy
* Light
* Handy
Figurative Adjectives:
* Defining (as in "a defining marker in history")
* Significant
* Landmark
* Symbolic
The best adjectives to use will depend on the specific context and what you want to emphasize about the marker.