One account only is the best choice be cause it will turn to cheat when you using 2 signature on the same profiles. Although you can join to other signature campaign with another account you may have but becareful, you could be block because cheat detected.
That is the truth. I've seen people who change signatures on middle of their campaign because they want to get stakes from 2 campaigns and that is their biggest mistake because all of their efforts will be in vain because the bounty team will find out who cheats and they will get removed and banned from the spreadsheet easily.
But you have so many other campaigns other than signature campaign like content creation,social media and translation campaign where you can participate on multiple campaigns at the same time. 