The last phase of this puzzle (like the 2004 con's Saturday night 
extravaganza, which I helped write and which I intended this as
a warmup to) was very site-specific: You had to go to the location
specified at the con hotel (the Marriott at Kendall Square), and
find a painting there; the painting depicted coins around its
perimeter in the same positions as the circles in the grid, and
the circled V in the grid corresponded to an old V nickel.