I want to use the current text's dimensional properties for constructing an inline TikZ image, such as an icon.
The properties I have in mind for use are
\height
\depth
\totalheight
as described here.
What I want to achieve is something like the following, but instead of using ex units, want to be sure the drawing fits into the line exactly.

\tikz[baseline={1ex}] \draw[draw=black, fill=blue, rounded corners] (0,0) rectangle (5ex,3ex) ;
Signal
Please observe that this code lets the drawing start too low (below the "g" in "Signal") and end too high (above the "S" in Signal).

\vphantom? One that does not rely on the looks of the current font (particularly the S and g letters) for spanning all the way from top to bottom? – derabbink Dec 11 '13 at 13:54calcalso provides\heightofand\depthofmacros, but they again rely on the font. – Dec 11 '13 at 14:23