All infantry divisions that fought in WWI had their unit insignia painted on their helmets.
In WWII, only some infantry divisions chose to have their division patch painted on their helmets ([url=http://www.steelpots.com/]steelpots.com[/url]). A number of infantry divisions had their combat brigades paint a regimental symbol on a side of their helmets.
The following is an excerpt from an article explaining regimental symbols of the 101st Airborne Division in WWII.
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[b]Helmet Stencils[/b]
One of the distinctive forms of insignia worn by the 101st Airborne in WW2 was Helmet Stencils. After the chaos of an Airborne landing, with personnel of various sub units mixed together on the ground, quick assembly by units was essential for carrying out a mission. Symbols readily visible on helmets were expected to facilitate the re-assembly process. Each regiment and the support battalions had a symbol stenciled in white paint on the left and right side of the helmet.
In England before the Normandy Invasion, these were first applied to the steel pots only. Later, stencils were also applied to helmet liners. Although some regimental stencils were applied without a battalion 'tic', a small dash was usually added at the 12 oclock, 3 oclock, 6 oclock, or 9 oclock positions, to designate battalions, in clockwise order. HQ was at the top, 1st Bn at the 3 oclock position, 2d battalion at the 6 oclock position, and 3rd Bn at the 9 oclock position.
The Infantry regiments were represented by playing card symbols, Diamonds for 501, Hearts for 502, Spades for 506th, Clubs for the 327th Glider Infantry. Due to a foul-up the entire 3rd Bn of the 506th jumped into Normandy with their Bn tic in the 1st Bn position (3 oclock, instead of 9 oclock), This was corrected later in WW2. All units also utilized the standard ETO stencils of vertical and horizontal bars along the rear of the helmet for officers and non coms These markings were clear signals to enemy snipers and were sometimes covered or eliminated in combat. The members of divisional HQ wore a square stencil with tics to designate Signal Co., MPs, Ordinance, etc.
[img]http://www.101airborneww2.com/Griswold.jpg[/img]
Photo 1) depicts LTC George Griswold as commander of 3rd Bn 501 PIR in early 1945, wearing the diamond stencil with tic at 9 oclock.
[img]http://www.101airborneww2.com/C502helmet.jpg[/img]
Photo 2) depicts an unknown member of C/502 awaiting the postwar 'pay jump' at Auxerre, France in 1945. As with all 1st battalion helmets, the 'tic' appears at the 3 o'clock position in relation to the regimental symbol. Photo courtesy Frank Miller.
[img]http://www.101airborneww2.com/Chief.jpg[/img]
Photo 3) depicts "Chief", a Native American member of D/506th wearing spades with a tic at the 6 oclock position for 2d Bn. Photo c/o Louis Truax
[url]http://www.101airborneww2.com/insignia3.html[/url]
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I couldn't find anything online about division patches on helmets after WWII.