Here is a quick, cheap, and simple way to solve the problem, and remove the stain
There are all kinds of cleaning products out there on the market, Autoglym, Turtlewax (other brands are available ) etc ..
However, I have discovered that there is an easier and simpler way to remove this stain, that will not require expensive solutions
or alot of time.
Firstly, make sure your car is clean, so that you do not scratch the surface of the paint.
Find a cloth....I find old tatty towels, or tea towels are the best...but again make sure the cloth is clean so that no particles are in it which could scratch the surface of the paint...you can also use microfibre cloth but again it needs to be clean.
Then, from the kitchen, put a squirt of washing up liquid on the cloth...I use Surcare at the moment but Ecover and Fairy also give a perfect result...and of course other brands can be used....
Use your finger to work the washing up liquid along the stain....and it lifts off remarkably easily
Rinse well with water...and polish your car using the products of your choice :-)
Here is the before....from steffross's car....and the after from George
as you can see perfect result
ps this is washing up liquid used for washing the dishes in the sink, not cream cleanser or laundry liquid