Side handle

The Mondasian's side handles functioned as the emotional inhibitor. (TV: World Enough and Time)

Side handles were the distinctive pair of handles which were located atop the Cyber-helmets of most Cybermen. (PROSE: Doctor Who and the Tenth Planet, TV: The Age of Steel, The Time of the Doctor)

Recognition

Upon discovering the Cybermen in Pete's World, Rose Tyler realised that she had seen the head of a Cyberman before, recalling the distinctive handle shapes. (TV: The Age of Steel)

The Eleventh Doctor gave the name Handles to his Cyber-helmet companion. (TV: The Time of the Doctor)

Variants

Cyber-Controllers were typically distinguished by their enlarged craniums which lacked side handles. (TV: Attack of the Cybermen)

Cyber-Leaders were distinguished by their black side handles. (TV: The Pandorica Opens)

In the case of the Mondasian Cybermen, the handles were a attachable headset which functioned as an emotional inhibitor, which was lacked by the first Mondasian patients. (TV: World Enough and Time) Conversely, the emotional inhibitors of the Cybermen from Pete's World were located within their chests. (TV: The Age of Steel)

Cyber-Controllers, such as the one who resided on Telos, were generally distinguished from their subordinates in that their helmets sported an enlarged cranium which forgone the handles. (TV: The Tomb of the Cybermen, Attack of the Cybermen) Conversely, John Lumic, the Cyber-Controller of Pete's World, had a Cyber-helmet with handles. He was distinguished by his brain which was visible behind the forehead's casing, and a set of four blue lights in each eye. (TV: The Age of Steel)

In both N-Space and Pete's World, Cyber-Leaders were typically distinguished by their black handle bars. (TV: Earthshock, Army of Ghosts) The leader of the CyberNomads had a black helmet with only a silver faceplate. (TV: Revenge of the Cybermen)

Cybershades had bronze Cyber-heads. Like their Cyberman superiors, they had piping like handlebars connected to their heads, except they angled diagonally like the ears of an animal. (TV: The Next Doctor)

The CyberKing's human control unit was converted using a side handle headset that connected the subject's mind to the CyberKing, changing their speech patterns and their eye colour throughout the process. Once the conversion was complete, the controlling unit could operate the CyberKing's movements and in the case of Mercy Hartigan could even take command of the Cybermen themselves. (TV: The Next Doctor)

Uniquely, Cybermen whom participated in an alternate Last Great Time War had helmets whose side handles pointed down rather than upwards. (COMIC: Prologue: The War Doctor)