Why does a 1953 US 5 dollar bill have a red seal on it?

The banner across the top of your bill identifies it as a United States Note. These bills were printed with red ink to distinguish them from silver certificates (blue) and Federal Reserve Notes (green).

US Notes were issued directly by the federal government rather than through the Federal Reserve System. The two kinds of currency served the same purpose so production of US Notes was suspended in 1971 to save on printing and distribution costs.