I have gotten Mark several times in person, and this looks consistent (for the most part). His signature is really strange, however, and it can be really tough to authenticate. I would say I'm leaning towards authentic on this one, but he's just so difficult to authenticate I can't be 100% certain. I'm sure others will chime in as well. Do you own this piece? Where/how was it acquired?
This could very well be authentic as others have stated, but i personally wouldnt buy it. The Mark signatures i typically see are typically larger as A.B. pointed out. The few that i have in my collection also dont seem to match up with this one on how the overall signature is formed. There is just something about it that looks off to me. But as pointed out, his signature is so weird and very easily forged in my opinion, so its really hard to tell. It may be authentic, but their are a few red flags that i see that would make me stay away from it. But i hope it turns out real if you decide to buy it.