This paper presents abundances for 12 red giants of the old open cluster Collinder 261 based on spectra from the Very Large Telescope UVES. Abundances were derived for Na, Mg, Si, Ca, Mn, Fe, Ni, Zr, and Ba. We find that the cluster has a solar-level metallicity of [Fe/H] = -0.03 dex. However, most α- and s-process elements were found to be enhanced. The star-to-star scatter was consistent with the expected measurement uncertainty for all elements. The observed rms scatter is as follows: Na = 0.07, Mg = 0.05, Si = 0.06, Ca = 0.05, Mn = 0.03, Fe = 0.02, Ni = 0.04, Zr = 0.12, and Ba = 0.03 dex. The intrinsic scatter was estimated to be less than 0.05 dex. Such high levels of homogeneity indicate that chemical information remains preserved in this old open cluster. We use the chemical homogeneity we have now established in Cr 261, the Hyades, and the HR 1614 moving group to examine the uniqueness of the individual cluster abundance patterns, i.e., chemical signatures. We demonstrate that the three studied clusters have unique chemical signatures and discuss how other such signatures may be searched for in the future. Our findings support the prospect of chemically tagging disk stars to common formation sites in order to unravel the dissipative history of the Galactic disk.