General Discussion

That emblem can be traced all the way back to the early 19th Century

Prussia

Use of the Totenkopf in Germany as a military emblem began under Frederick the Great, who formed a regiment of Hussar cavalry in the Prussian army commanded by Colonel von Ruesch, the Husaren-Regiment Nr. 5 (von Ruesch). It adopted a black uniform with a Totenkopf emblazoned on the front of its mirlitons and wore it on the field in the War of Austrian Succession and in the Seven Years' War. The Totenkopf remained a part of the uniform when the regiment was reformed into Leib-Husaren Regiments Nr.1 and Nr.2 in 1808. The symbol was then granted 3 years later to the Spanish Army’s 8th Light Cavalry Regiment “Lusitania”, who were nicknamed “Los Dragones de la Muerte” (the Dragons of Death) and were granted use of the skull after the infamous Battle of Madonna dell'Olmo in 1744, where they suffered great casualties.

Brunswick

Totenkopf badge worn by the Brunswick Leibbataillon ("Life-Guard Battalion&quot at the Battle of Waterloo in 1815
In 1809, during the War of the Fifth Coalition, Frederick William, Duke of Brunswick-Wolfenbüttel raised a force of volunteers to fight Napoleon Bonaparte, who had conquered the Duke's lands. The Brunswick Corps was provided with black uniforms, giving rise to their nickname, the Black Brunswickers. Both hussar cavalry and infantry in the force wore a Totenkopf badge, either in mourning for the duke's father, Charles William Ferdinand, Duke of Brunswick-Wolfenbüttel, who had been killed at the Battle of Jena–Auerstedt in 1806, or according to some sources, as a sign of revenge against the French. After fighting their way through Germany, the Black Brunswickers entered British service and fought with them in the Peninsular War and at the Battle of Waterloo. The Brunswick corps was eventually incorporated into the Prussian Army in 1866.

German Empire

The skull continued to be used by the Prussian and Brunswick armed forces until 1918, and some of the stormtroopers that led the last German offensives on the Western Front in 1918 used skull badges. Luftstreitkräfte fighter pilots Georg von Hantelmann and Kurt Adolf Monnington are just two of a number of Central Powers military pilots who used the Totenkopf as their personal aircraft insignia.

Weimar Republic

The Totenkopf was used in Germany throughout the interwar period, most prominently by the Freikorps. In 1933, it was in use by the regimental staff and the 1st, 5th, and 11th squadrons of the Reichswehr's 5th Cavalry Regiment as a continuation of a tradition from the Kaiserreich.

US Military

The U.S. military does not have an official, standard-issue "death's head" insignia. However, the skull and crossbones (Totenkopf) motif has occasionally appeared in unofficial unit patches and unofficial morale gear—though these have occasionally sparked investigations or controversy due to the symbol's historical ties to Nazi Germany's SS units.

UK
The death's head (skull and crossbones) is a historic military emblem used by the British Army, famously featured on the cap badge of The Royal Lancers (and their antecedent units, the 17th Lancers and the 17th/21st Lancers).