July 4th Parade Protocol

[CrazyEyez]

Seen last night, 7/3, circa 6pm along my city's parade route:

Unmanned blankets laid out on the sidewalk, with rocks and/or folded chairs holding them in place.

a) Were I to have attended the parade and arrived say, 45 minutes early, and found said unmanned blankets, am I within my parade rights to toss them aside and claim the space for mine own?

b) If not, how early is it acceptable to start leaving blankets? 24 hours?

c) If the rule is that you must be there in person to stake out a spot, can one family member arrive early and lay claim on behalf of the entire family? In this case, how much territory may one person claim (in square feet) for yet-to-arrive guests?