  A small subset of optically selected radio-quiet quasars showing weak or no
emission lines may turn out to be the elusive radio-quiet BL Lac objects, or
simply be radio-quiet QSOs with a still-forming/shielded broad line region
(BLR). High polarisation ($p$ $>$ 3$-$4$\%$), a hallmark of BL Lacs, can be
used to test whether some optically selected `radio-quiet weak emission line
quasars' (RQWLQs) show a fractional polarisation high enough to qualify as
radio-quiet analogs of BL Lac objects. Out of the observed six RQWLQs
candidates showing an insignificant proper motion, only two are found to have
$p$ $>$ 1$\%$. For these two RQWLQs, namely J142505.59$+$035336.2,
J154515.77+003235.2, we found polarisation of 1.03$\pm$0.36$\%$,
1.59$\pm$0.53$\%$ respectively, which again is too modest to justify a
(radio-quiet) BL Lac classification. We also present here a statistical
comparison of the optical spectral index, for a set of 40 RQWLQs with
redshift-luminosity matched control sample of 800 QSOs and an equivalent sample
of 120 blazars. The spectral index distribution of RQWLQs is found to differ,
at a high significance level, from that of blazars and is consistent with that
of the ordinary QSOs. Likewise, a structure-function analysis of photometric
light curves presented here suggests that the mechanism driving optical
variability in RQWLQs is similar to that operating in QSOs and different from
that of blazars. These findings are consistent with the common view that the
central engine in RQWLQs, as a population, is akin to that operating in normal
QSOs and the primary differences between them might be related to differences
in the BLR.
