  By extending the notion of Lie derivative to distribution-valued tensor
fields of order $m$, Lie derivatives with respect to $C^k$ vector fields,
$k\geqslant m+1$, can be shown to be well defined. Geometric symmetries,
definable in terms of these Lie derivatives, can then be considered. In
particular, for spacetimes of low regularity, geometric symmetries generated by
vector fields of regularity as low as $C^1$ are definable. We find that the
conformal algebra of the impulsive plane wave spacetime (with $+$ polarization)
described by the continuous Baldwin-Jeffery-Rosen form of the metric has the
maximal dimension seven. The curvature of this metric is well defined as a
distribution and since this spacetime is Ricci-flat, we show that all the
vector fields in the conformal algebra are special curvature collineations. We
find also the general form of these last ones. Finally, we find the conformal
Killing vector fields of this spacetime when using the distributional Brinkmann
form of the metric.
