road_marking=* is a somewhat chaotic tagging scheme because the original proponents left it fairly open-ended; many who later used it didn’t really coordinate the values. Are you asking about real-world terminology to help determine a correct tag that might not be in use yet?
Terminology might differ from country to country. In the U.S., traffic engineers usually use the following terms for markings:
| Pattern | Term |
|---|---|
////////// |
Diagonal |
\\\\\\\\\\ |
Diagonal |
XXXXXXXXXX |
Crosshatch |
<<<<<<<<<< |
Chevron |
>>>>>>>>>> |
Chevron |
The 
sign is located at the physical gore at the beginning of the grassy island. In front of it is a neutral area with diagonal markings. The tip of the neutral area is the theoretical gore, because it would be a real gore if a physical separation begins there.
The U.S. and some other countries typically use chevron markings for neutral areas. I guess that’s why road_marking=gore_chevron is one of the more popular road_marking=* values. But you’d need to use something else like gore_diagonal or somesuch since the marking isn’t a chevron.
As it happens, Poland is one of the countries that assign numeric codes to road markings, so you might use road_marking=PL:P-21 by analogy with road_marking=GB:1003A for dashed give way lines.