Non veni pacem mittere, sed gladium.
The t-shirt terrified their enemies.
It was the bulging muscles underneath.I take issue, however, with the use of the elder futhark. The actual Vikings would have used the younger futhark, so this writing on the tee shirt is inauthentic. I believe modern people simply tend to like the elder version as it's more consistent with what they think of as a proper alphabet.