How do I get the Springfield sign?

Apparently it’s available from level 1 yet I’m level 45 and I can confirm after endless searching in all tabs that it’s not there for me to buy for 170 donuts. Do I need to have completed a certain quest to be able to build it or is this item gone from the game? Another quick question - what’s the best way to increase my % earned on tasks? And is this ‘bonus’ money, or does it actually change the reward you get from the tasks? Like a 12 hour task, in the menus, says it rewards $420 yet I already have 8% extra, so am I getting 420 or 453? (8% increase) thank youuu