To my knowledge, in Urdu, ک is written without the *humza/squiggly sign.

In Arabic, in Holy Quran when ک is written in full, whether in Indo-Pak script or Uthmani script, it has the squiggly sign on it. (This sign is not written when ک is followed by a joining letter, as in the second ک in the same phrase below.)

ذٰلِكَ الْڪِتٰبُ لَا رَيْبَ

To check the usage in today's Arabic, I put two simple Arabic words ذالک and تلک in a search engine and most entries showed the ک with the squiggly sign, but there was one entry I saw that didn't have it.

So, I think if someone is writing Urdu with the squiggle on ک, they're using their Arabic keyboard or are using Arabic script on purpose. I think if one has a choice, one shouldn't use the squiggle. If someone else is using it, I'll give them the benefit of the doubt that they know what letter it is, they're just being unnecessarily (if not inappropriately) stylish with it.

Perhaps there is some old Urdu script that does use the squiggle on the ک, I don't remember seeing one though.

*P.S. I'm not sure if that symbol on ک can be called a 'humza' as it looks different then a regular humza...a "squiggle" perhaps? If the symbol is indeed a different sign then 'humza' and people are adding a 'humza' on their ک, then that could be considered wrong.



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Note added at 1 hr (2010-11-14 20:46:09 GMT)
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Correction: In second last line, please read the first "then" as "than"...so it would read:
"If the symbol is indeed a different sign than 'humza' and ...."