The T-merke - literally T-mark - is the painted red letter T that marks DNT trails across Norway. It is the country's universal hiking signage system: a single bright red T painted on a rock, a tree or a wooden stake at intervals close enough that the next mark is always visible from the previous one, even in poor weather. The system is a century old (the DNT adopted standardised T-marking in the 1890s) and now extends across approximately 30,000 kilometers of marked Norwegian mountain trails.
The marks are hand-painted by DNT volunteers every summer. Each regional DNT chapter is responsible for its own section of network; the painting is done by small crews who walk the trails with red paint, brushes and stencils, refreshing marks that have weathered and adding new ones where needed. The work is voluntary - DNT members donate roughly 25,000 hours of trail-marking labour each year - and is one of the most visible expressions of the wider Norwegian outdoor culture.
What the T-merke means in practice for a walker: the trails are unusually well-marked by international standards. On a clear day in good conditions, you can usually see the next T from the previous one, sometimes from the one before that. In poor weather (fog, snow, low cloud), the marks remain the single most reliable navigation aid; the standard practice is to walk from mark to mark, not lifting your eyes from the next visible T until you reach it. The same system is used in winter for ski routes, with the marks supplemented by tall Y-shaped birch poles (kvister) where the snow buries the rock-painted Ts.
The T-merke is also a small visible expression of the broader principle that the Norwegian mountain country is a public commons. It is painted by volunteers, on rocks that nobody owns, leading to huts that anyone can use, across land that anyone can walk under allemannsretten. The system genuinely works because the underlying culture treats it as worth maintaining. International visitors used to paywalled or privately-managed mountain access tend to find this culturally striking once they spend a few days noticing it.