Many Chasidic groups have a particular siddur that is used by most in that group. Does Satmer have such a siddur?
Davening in a Satmer shul in Boro Park, I noticed the siddurim used there were not the typical dimensions I was used to seeing. On the first page the publisher explained that it was made that way in order to fit the (pretty narrow) shtenders (pews).
I don't remember seeing anything unusual about the siddur itself.
On Yomim Tovim many of them use the Machzor Divrei Yoel which details all the customs of the Divrei Yoel.
That is right "The Rebbe R' Yoel Teitelbaum himself davened from סדור תפילה ישרה וכתר נהורא." See here: "Historic Prayer Book Used by Satmar Rebbe Joel Teitelbaum OB"M" http://www.ebay.com/itm/222625469643?ul_noapp=true