I know what spawn sequences are but when you go to choose the items spawn sequence there are positive integers and negative integers. What are negative spawn sequences?
In the Reach strategy guide's Forge section, it says that Rally checkpoints are RACE_FLAG items (yes, Race checkpoints) with a Spawn Sequence of -1. (This is incorrect; they actually use Rally's RALLY_FLAG label and the Spawn Sequence option does nothing.) So far, negative values are unused. It is known that Reach's new gametype engine uses a script interpreter, so Bungie could design future gametypes that use negative values.