Using the CLEO II data sample, with an integrated luminosity of 1.8 ${\mathrm{fb}}^{\mathrm{-}1}$ at and near the Υ(4S) resonance, we have observed a signal for ${\mathit{D}}^0$→${\mathit{K}}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$, which could be due to either ${\mathit{D}}^0$D${\mathrm{¯}}^0$ mixing or doubly Cabibbo suppressed decay, or a combination of the two. We find scrB(${\mathit{D}}^0$→${\mathit{K}}^{+}$${\mathrm{\pi }}^{\mathrm{-}}$)/scrB(${\mathit{D}}^0$→${\mathit{K}}^{\mathrm{-}}$${\mathrm{\pi }}^{+}$)=0.0077±0 .0025(stat) ±0.0025(syst).

• Received 2 December 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.1406