  In this letter, we find a peculiar characteristic mass spectrum of the
isoscalar $D^*\bar{D}^*$ molecular systems, which can be applied to identify
charmoniumlike molecule. By checking the reported $XYZ$ data of the $B\to XYZ+
K$ decays, there exists the evidence of double peak and single peak structures
below the $D^*\bar{D}^*$ threshold in the $J/\psi\omega$ invariant mass
distribution of the $B\to J/\psi\omega K$ process and in the $J/\psi\eta$
invariant mass distribution of the $B\to J/\psi\eta K$ process, respectively.
Here, the double peak structure is due to isoscalar $D^*\bar{D}^*$ molecular
states with $J^{PC}=0^{++}$ and $2^{++}$ while the single peak structure may
correspond to isoscalar $D^*\bar{D}^*$ molecule with $J^{PC}=1^{+-}$. Due to
the similarity between the $D_s^*\bar{D}_s^*$ and $D^*\bar{D}^*$ systems,
similar double peak structure is predicted here, which can be accessible by
future experiment when analyzing the $J/\psi\phi$ invariant mass distribution
of the $B\to J/\psi\phi K$ process.
