&gt; <i>b) Thank-you light on the back of a car. Maybe blue.</i><p>I still wonder why those aren&#x27;t popular:<p><a href="http:&#x2F;&#x2F;www.thinkgeek.com&#x2F;product&#x2F;d138&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.thinkgeek.com&#x2F;product&#x2F;d138&#x2F;</a><p>Is there a regulatory reason against placing something like it behind your rear windshield?