Insignia of rank may have varied from regiment to regiment.
According to 47TH FOOT IN NORTH AMERICA, 1772-1781
Non Commissioned Officers
The uniform distinction for a corporal was a shoulder knot of white cord on the right shoulder, a vestige of the extra slow match carried in earlier days. By the 1780s, regiments shifted to a single white silk epaulette. Other than the knot/epaulette, corporals wore the same uniforms as privates.
Sergeants wore coats of slightly better cloth than privates, scarlet not dull madder red. Sergeants’ wore hats trimmed with silver lace and their coats trimmed with plain white lace instead of the regimental pattern. They also wore a red wool sash with a stripe of the regiment’s facing color woven in the middle. Regiments with red facings wore a white stripe. For duty on more formal occasions a sergeants carried a halberd and short sword, but for most duty in America, sergeants carried a musket with bayonet.
Officers wore coats of fine scarlet faced with their regiments' color. Officers had their coats and hats trimmed in either gold or silver metallic lace depending on their regiment’s designated metal. On duty, officers carried a sword and wore a matching metal gorget around their neck. Officers tied the gorget, a vestige of medieval armor, with a silk ribbon of the facing color. Company-level officers, up to captain, wore a metallic lace epaulette on their right shoulder. Officers above captain, as well as grenadier and light company officers, wore two. Many officers in America wore plain unlaced coats and hats on duty, often carrying a light musket, or fusil.
According to Uniforms of the 68th Light Infantry
When the 68th was converted to a Light Corps in 1808, a number of changes took place in its uniform.
One badge of rank work by officers on duty was a survivor from medieval times. The 'gorget' was originally a crescent-shaped piece of armour worn to protect the throat, but by Napoleonic times it had reduced in size to become purely ornamental. It still survives today as the red gorget patches on the uniform of a Staff-Officer.
Officers of the Light Infantry had a unique system of rank-marking. Because they had to be identifiable from both sides, whilst skirmishing in open-order, all markings had to be worn on both shoulders in the form of a pair of 'wings', the length and thickness of the bullion-edging distinguishing subalterns from captains. Field officers (Majors and above) wore a pair of epaulettes superimposed upon the wings; the rank of Major being indicated by a star on each shoulder; a Colonel by a crown. In the case of the 68th, the bullion was in silver, for all officers. Officers wore a variety of footwear; in the Light Infantry many adopted Light Cavalry style hussar boots. Light Infantry Officers carried a Light-Cavalry sabre in place of the usual straight Line-Infantry sword. This was fastened to a shoulder-belt, as was a whistle on a chain attached to a lion's-head boss. The whistle, also carried by Sergeants, (and still worn in the modern Light Infantry as the "Inkerman Chain"), was used to relay orders over short distances in the field. The modern system of sleeve chevrons for NCO's had been adopted early in the Napoleonic Wars. These stripes were worn on a piece of material of the facing colour on both sleeves.