He is talking about Symbol of the Sniper skill, which can be used (in Interlude client) using Battle Force and Spell Force skills, also in order to be used some items are required: Magic Symbol and Battle Symbol.
Depending on the skill the level of the Force you need might be higher or lower, for example Symbol of the Sniper requires a Battle Force level 2 and 1 Battle Symbol.
Those 2 skill are learned at level 80 depending on the char type (fighter, mage) and for every char who cast it you earn a level.