Young leaves and dead leaves

Young leaves and dead leaves.

In Japan you can get a driving license when you have turned  18 years old. Your first driving license is valid for 2 - 3 years from the day of the issue until your second birthday date. Then you need to renew it every three - five years, depending on your accident history and age.

When you get your first license, it is obligatory to put the "beginners sign" ("wakaba mark") on your car during the first year of driving. That sign looks like a young leaf, green with yellow, and symbolizes "the green, inexperienced person at the wheel". The purpose is to notify other drivers about your poor driving experience, so they could be aware of you or, on the other hand, seeing the sign, people might be nice and letting you in (which is not likely in real).  
In 1997 the Road Traffic Law of Japan in addition to the "beginners sign" issued a law to use "elderly driver" ("koreisha mark") signs on cars driven by people over 75 as an obligatory matter, and ask people over 70 to endeavor to use this sign. The "elderly driver" sign was designed as an autumn leaf, yellow and brown, which soon became a target of irony, because it obviously symbolized  a dried leaf or a fallen leaf. Elderly didn't want to drive with this dead leaf mark on their cars, finding this new law rather insulting. In 2011 the government finally changed that "aged driver" sign to another one, a four-leaf clover, a lucky mascot.

The average age of Japanese is getting higher every year. People stopped getting married and having babies, on the other hand the elderly got healthier and are now living longer. So the elderly society grows bigger and stronger. Now they laugh about age and death. Some people started to love  the  old "dead leaf" mark, because it shows their long experience not only of driving but of life itself. So the "experienced driver" leaf became even more popular than the “beginners" young leaf.

I just wonder how many people would be nicer to a car with either of those signs? I tried to drive with the "beginner sign" and I felt like everyone tried to overtake or cut in, thinking that I might be too slow or too dumb to counter their intentions. I didn't feel any kind of understanding or assistance. It was rather dangerous to drive with usual speed. What kind of mark should I put on my car to avoid such abuse? The only way is to look like a police car, I think. 
(A comment from my friend: "Or drive an old large car with lots of dents on it, letting everyone know you've hit a lot of cars and it doesn't bother you"). A tank might do, too?