Hi chetan88,
Respectfully; yes, it is normally very easy to tell when the poster's first language is not English. Your own post here contains two misspellings. As someone else here said, it's actually kind of charming, just as when someone you meet speaks with an accent and somewhat imperfect pronunciation or word choices.
However...as motown-l said, it' is really surprising to see the gross errors in spelling and grammar that are made by posters here who are obviously American. These posters often have extensive knowledge of electronics and other subjects requiring good or better intelligence; yet they don't know the difference between there and their. They also write run-on sentences without regard to punctuation; or they use commas too often in the wrong places. We all make spelling errors and occasional grammatical or punctuation errors. I'm speaking about consistent misuse by presumably educated people who own systems that are worth quite a bit more than my home.
In the past when I have pointed this out occasionally, I have been called the grammar police, etc; and so have others that pointed these things out. I still think that there is value in writing things as correctly as possible, because it makes it much easier to read.