[SUGGESTION] New Thief ability: "The Mark"

A good thief always chooses a "mark" -- a target -- based on intel and risk-assessment. Since the Thief's F1 and F2 abilities are already allocated to Steal and using the stolen item, this ability would make use of F3 by default. Here's what the skill would look like:

The Mark40s cooldown (skill goes on cooldown when used, not when the mark expires)

Place a mark above your target that lasts for 8 seconds or until you attack the marked target. The mark will appear to you and nearby teammates even when your target enters stealth or summons illusions. While in Stealth, you move faster toward the marked target, and your first melee attack is unblockable. Using Steal against the marked target does not count as an attack even if it deals damage or applies conditions.

Why? Well, I see this primarily as a flavorful way to help Dagger Thieves become relevant again in PvP, with the added bonus of giving Thieves some utility against (mainly) Mesmers, who are just broken right now. Backstab is currently extremely difficult to land with the 1s cooldown, and who better than a Thief (the master of non-magical deception) to call out an enemy Thief or Mesmer (the master of magical deception) for her teammates. Currently, Thieves tend to operate as mobile cappers in 1v1 and +1 scenarios, so the fact that only nearby teammates (not sure what I would consider a fair range, but envision teammates on/near the same capture point only) can see the marked target means this isn't going to alert everyone on your team to where an enemy Thief or Mesmer is, and if they change course upon going stealth, the only way your teammates will know if if you tell them, "Hey, you've got an incoming stealther..." Also, the mark itself is visible, but that doesn't affect the mechanics of in-game targeting, so any skill someone uses that would cause you to lose target of them would still work in that regard; it would just be a lot easier for people to see where the marked target went, or which one is the real mark, in the case of Mesmers with all their illusions. You'd still have to re-target them by clicking or tabbing through, though.

Thoughts? Criticisms?

restricting targeted skills to a marked stealthed opponent doesnt do too much, as most stuff ingame is AoE. why only unblockable melee attacks ? are there any relevant strong single hit , range openers for a thief that would be too strong if they were made unblockable? DJ might be but that is easily dodged and not relevant for spvp as malice build up is too slow.

aside from that cant talk much about the mode itself, so do you want that skill exlusively to sPvP mode or to all modes ? should there be differences?because this buffs mainly stealth openings. stealth, especially long(or perma) stealth is really strong in solo/smallscale WvW and this would buff this even more.

I see this as a way to buff a Thief's utility and help melee (specifically Dagger) Thieves in sPvP. It doesn't do a whole lot in solo, but I can kinda see how it might be really strong in WvW.