  This paper presents abundances for 12 red giants of the old open cluster
Collinder 261 based on spectra from VLT/UVES. Abundances were derived for Na,
Mg, Si, Ca, Mn, Fe, Ni, Zr and Ba. We find the cluster has a solar-level
metallicity of [Fe/H] = -0.03 dex. However some alpha 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, Hyades and
the HR1614 moving group to examine the uniqueness of the individual cluster
abundance patterns, ie. 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.
