A few things I found after reading this comment and looking closer at the drawings:

This new drawing: http://releases.walkingwallofwords.com/products/the-book-cipher-sings-3 looks an awful lot like this print Jeff released a while back: http://imgur.com/MjFuryX -The key differences here are the "DOUBLE" text in the mountains and arms, and "3RD" text in the hair (or flames) on the sides of the faces, under the table, and ringed planet on their chest.

In this drawing: http://releases.walkingwallofwords.com/products/the-book-cipher-sings-4 -“Magicicada” and “Cassini Huygens” are printed underneath the table. Magicicadas have either a 13 or 17-year lifespan. Jeff started officially touring again in 2011, about 13 years after NMH disbanded. Remember the 17-year lifespan. -As mentioned by maldenfilms above, Cassini-Huygens is an unmanned spacecraft sent out about 18 years ago (Aeroplane was released about 18 years ago). It was also the first spacecraft to ever orbit Saturn (three of these new drawings feature ringed planets with 3RD or 1ST 2nd 3RD printed in them). Its expected retirement is 2017. -17 comes up twice here, and hey, both arms in the drawing have 1-2-3-4-5-6-7 drawn on them. Could be hinting at a 3rd album in 2017?

I know, I know, I know, there is a very real chance there are no real connections here, or maybe there are but they have nothing to do with a new album. I know Jeff has said multiple times there will never be a NMH album, but things can change. Jeff has a very interesting mind and could have just included a cool puzzle unrelated to his music in these drawings. Who knows. Either way, cool artwork, glad Jeff continues to create.