As you've been able to find out from this report, lead is indeed present in some lipsticks even at significantly high levels for some popular lipsticks as the study from The Campaign for Safe Cosmetics indicated.
However, a fully equipped laboratory with trained staff is needed to break down the components that make up the lipstick, and then evaluate the amount of lead if present.
These e-mails claim that you can put some lipstick on your hand, use a gold ring to scratch on the lipstick, and if the lipstick color changes to black then you know the lipstick contains lead.
The handy home test for lead in lipstick touted in the emails is bogus. Certain metals, including gold, may leave a dark streak when scratched on various surfaces, but this is an artifact of the metals themselves, not an indicator of a chemical reaction with lead or any other substance.
You can view a couple of these e-mails posted by David Emery.
On the same note, there are "lead test kits" that are being sold to consumers for use in detecting the presence of lead.
The two types of test kits, reported by CPSC ( Consumer Product Safety Commission ) that are currently available are based on chemical reactions of either the rhodizonate ion, which produces a pink or red color in the presence of lead, or the sulfide ion, which produces a gray, brown or black color in the presence of lead.
However, a CPSC staff study has found that the "Home Lead Test Kits" are unreliable.
Many of the tests performed using the kits did not detect lead when it was there (false negatives); some indicated lead was present when it was not (false positives). Of 104 total test results, more than half (56) were false negatives, and two were false positives.
You can view CPSC's results in their report, which is a [pdf] file.
In summary, a home detection test would be unreliable as it might give you false results. If you're concerned about lead in lipsticks, best thing you can do is get a lipstick free of lead and any other chemicals that may harm you, or in other words, get an organic lipstick.