This has irritated me for a long time. I consider it a bug, but regardless I'd like to see it changed to reflect only the silenced status of the alias call. Why anyone would need an identifier to evaluate whether or not they explicitly typed a period in front of a command is a mystery to me.

To clarify, I think it ought to work like this:
/testShow:

echo $show = $true
.echo $show = $true

/.testShow:

echo $show = $false
.echo $show = $false

...because that's the only way that really makes it useful in scripting. Consider this a vote for change!

(also, be sure and fix echo -q to behave the same way if the code isn't shared with $show)