There are special commands for Laplace-Transformation Symbols in trfsigns package (see The Comprehensive 
 Symbol List, Table 81, page 40): \laplace  and \Laplace .
To use them with QuickLaTeX, just include trfsigns in preamble (local or global), e.g:
\[
[+preamble]
   \usepackage{trfsigns}
[/preamble]
  f(t) \laplace F(s) \qquad F(s) \Laplace f(t)
\]results in
      ![]()
Can you do that with other LaTeX plugins for WordPress :-)?

One Comment
Hi Pavel,
I tried copying those couple lines of code, but I get the following
http://kennychowdhary.me/test/?p=4.
How are you getting the display to be as sharp as wordpress.com’s latex? Are you using wordpress.org?
Thanks,
Kenny