  Due to the deflection of light by density fluctuations along the line of
sight, weak lensing is an unavoidable systematic uncertainty in the use of type
Ia supernovae (SNe Ia) as cosmological distance indicators. We derive the
expected weak lensing signatures of SNe Ia by convolving the intrinsic
distribution in SN Ia peak luminosity with magnification distributions of point
sources. We analyze current SN Ia data, and find marginal evidence for weak
lensing effects. The statistics is poor because of the small number of observed
SNe Ia. Future observational data will allow unambiguous detection of the weak
lensing effect of SNe Ia. The observational signatures of weak lensing of SNe
Ia that we have derived provide useful templates with which future data can be
compared.
