After the maintenance I'll take a look at some of the macro commands and see if there might be a good way. I would think there is a targeting order based on priority in the aggro list. Similar to <1> - <8> for targeting party members. If there is, could just do:

/mk attack1 <aggro1>
/mk attack2 <aggro2>
...

In theory this would work great, and would likely just open the sign box if a mark fails (no target to mark). This would also only work once there are enemies in your aggro list.

As for sequentially marking pre-aggro.... I believe there is a command in the abilities menu that goes forward target, and one for backwards target. There should be a / command for it, but I'm not familiar offhand.