Obviously, I cannot see that, even I cannot say that there exist some of its effects and I can observe them. But, a brain storm gives some of its characteristics.

Speed !

For example, sort the other senses according to their speed for gathering information, seeing uses light speed, hearing uses sound speed, smelling uses molecular travelling speed and etc.

Thus, a simple math says that, if there exist sixth sense, it should be faster than seeing. I prefer a negative referenced timing, which you can name it prediction.

Distance ! 

Another characteristic would be the distance.

You can see something from 200m, you can hear it from 40m, smell it from 10m, taste it or touch it when you are 0m far from it. Again, a simple math says that sixth sense should be able to provide information from further distances, and it can be anything (exponential fitting says 1.2 KM).

Logic! 

another characteristic: how logical is that! When you see something, information are very accurate, while if you touch something, there are many outliers and you have more space for guess. I mean, mathematically speaking, you have more points for interpolation when you see something, while less points when smell something.

Then, the accuracy of smelling will be less than seeing. Maybe that’s why romantic things are more related to senses that are not that strong, like “I recognize my lover from her sound or even her bodies perfume” is much more romantic than “I can recognize my lover if I see her”!!!!!

Relativity! 

It’s fantastic. So how about the relativity between observers in sight sense the difference between two image of one things by two observers is lower than two voice in hearing and its lower than smelling and tasting and touching. So the relativity between two observers in six senses should be lower than sight sense and it should be the same !

Conclusion : 

One beautiful thing about our sense is: the more useful the preceptor of that sense, the more sensitive, i.e. it is more probable to damage your eyes to damage your nose :-), there are many blind people but there are not many without smelling ability! So, the sixth sense should be really sensitive, we might have loose that at the birth, even before, because it is sensitive :-(. Where am I going??? Some one turn me offff