Almost without exception all "WWI" patches are post war. Most unit insignia was not approved until October 1918 and later. Uniforms with unit patches were generally the ones worn home or on occupation duty. The same is true of helmets and gas mask bags with insignia painted on them.They are very collectable however and the below picture shows some of the styles available. The patch at the top center is called a "Liberty Loan" patch and is of woven construction. The others are of embroidered construction.
The patch above has been identified as French made
Nothing is known about this patch other than that it came off a uniform belonging to a 27th Division soldier.
This patch on a captain's uniform was made from a "WELCOME HOME" ribbon similar to the one shown here
U.S. 2nd Corps patch. The figure on the left is an American eagle and on the right
is a rampant lion symbolizing their attachment to British forces