Hi Stewart.
"In God I trust" in Sanskrit. There are more translations possible, al with a slight difference of meaning.
If you want the western concept of God it will be better to use ishvara or parameshvara.
The most common translation will be ishvare vishvasimi or parameshvare vishvasimi.
Vishvasimi means also "I believe". parameshvaram shraddadhe is also very correct and a little bit archaich Sanskrit. You can also use deve. For vishvasimi you use the locative case, but for shraddadhe accusative. Devam shraddadhe is also nice and short.
The most common to use such an expression is to use the litteral "to take refuge".(accusative)
So Ishvaram / parameshvaram / devam sharanam gacchhami is the most common way to express this thought, however it means to take refuge in God.
See attachment for Devanagari script. If you want another Indian script, which is also used for Sanskrit, please let me know.
With regards, Vinayakan.