Site number
From LotR TCG Wiki
From the Comprehensive Rules 4.0:
Each minion is normally played to a certain range of sites beginning with the minion’s site number. If the minion is played to (or is currently at) a site that has a lower site number, that minion is roaming. The player must pay a roaming penalty by removing an additional two twilight tokens when playing that minion.
Block symbol has no effect on whether a minion is roaming or not.
A minion with a site number of 4 must remove 2 more twilight tokens to play at site 3 (or site 3[Tower]). If that same minion plays to site 4 (or site 4[Tower]), there is no roaming penalty. If he survives the fellowship’s first move to 3, he would no longer be roaming when the fellowship moves to site 4.