The Runebrand is both the name of the mark as well as the person. "Oh that village over there? They've a Runebrand." Or "That bandit's tattoo? That's a Runebrand. Be careful."
Runebrands are not feared with the same superstition as other forms of magic are in the world, as anyone can have one, but are still considered only a step above a Witcher. Having a Runebrand is also one of the few ways for an individual human to become more powerful in the Witcherverse, if they weren't turned into a Witcher or born as a Sorcerer.
In order for someone to become a Runebrand, they must have a Rune (which are one of the five Witcher signs) branded, tattooed, or scarred into their skin. The larger the brand, the more powerful it typically is. While the brand is being placed, it must also be "charged" by visiting a place of power of the corresponding sign. Each regular person can only have one Runebrand, and its powers are similar to those of a sign, but less overall powerful. Each Witcher-sign grants the Runebrand a different set of abilities.
Those with the Aard Runebrand gain some of its power and momentum. Attacks become more powerful, swinging faster and with more force then what the muscles alone could generate, and running speed and jumps are improved; blasted along with waves of force. This Runebrand is perfect for a heavily armored warrior. If the one with this Runebrand hits someone with a strong punch or blunt weapon, they can shove their enemy back with a small wave of force; significantly less powerful then an Aard cast by a Witcher, but enough to knock back or shove down a single foe with a good hit. This ability still requires stamina to cast and can be exhausting if used two or three times in a fight.
Those with the Axii Runebrand gain no new abilities, but instead gain some very powerful passive resistances to magic- specifically, mind controlling magic. Axii firstly makes its users almost totally immune to the Axii sign cast by Witchers, as well as gaining resistance to the mind controlling magic cast by sorcerers, witches, and even supernatural beasts. Many important nobles or powerful people have at least one Axii Runebrand, or may secretly be one themselves, to prevent themselves from being manipulated by mages and their ilk.
Those with the Igni Runebrand are naturally gifted with fire. This doesn't allow them to cast Igni in the way Witchers do, but instead grants a sort of "inner flame" that allows them to light small bundles of dry, flammable material on fire with a bit of concentration. For example, they could light a torch or an arrowhead dipped in pitch by just staring at it for a few seconds. Secondly, they are also highly resistant to the Igni sign, dragon fire, and fire in general; they can walk into burning buildings and only receive only minor burns while a normal person would have burnt to a crisp.
Those with the Quen Runebrand are resistant to physical pain and injury. This sign is more subtle then the others, given its nature as a purely defensive rune, but it simply makes the skin thicker and harder to cut. Thugs in cities and soldiers may carve this Rune into their skin for a defensive bonus, though without the proper rituals and planning it may have no effect beyond being a styled tattoo.
Those with the Yrden Runebrand are known to have the magical trapping rune active on themselves. Those who grab or touch the Yrden Runebrand will find their body suddenly struck with magical energy, slowing them down considerably and potentially dealing a small amount of damage. Those with this Runebrand can only focus it for a moment before impact, inflicting it on someone who harms them in that timeframe, but like any Runebrand it is far more exhausting for them to use their ability then for a Witcher to use a sign. Because this Runebrand is limited to working on those who touch or injury this Runebrand, it is often put on prisoners, cultists, or other fighters with more suicidal tenancies since this brand doesn't help them to survive longer in a fight.