Good good, we’ll get you all addicted soon….

Following Tufte’s advice to reduce the ratio of ink / data, you should:

Remove the border of the plot (“unset border”).
Only have ticks on the S and E sides (“set xtics nomirror”, “set ytics nomirror”).
Get rid of the redundant information in the key (“set nokey”) — and if you don’t, at least write “signup” or “sign up” consistently!
Probably get rid of the x-axis label (“unset xlabel”).
Not repeat the year in each x-axis label (this is a bit ugly, unfortunately, if you do want to put the year on one of them; I think you have to manually specify it).
Use a less horrid font — I think you do this by setting GD_FONT to the name of a Truetype font, less the “.ttf” suffix, in the environment, but there’s an example in the PledgeBank code anyway.

Also explain what you’re plotting — signups/day aggregated over what time period? Calendar days, I guess, but you don’t say. And to repeat something I’ve said before, I’d advocate also plotting the total number of signers as a function of time (on a separate, and separately-labelled, y-axis), since that gives a bit more information than the signup rate alone.