UNDER THE TABLE MANNERS

First of all, how does one distinguish between a casual touch that
doesn't mean anything, and one with intent?
 
Well, in my experience, watch out if the person across from you
very obviously takes off his or her shoe and then slams it on the
table in front of you.  Then, if he or she spins it and stops it
when it points at you, extends a forefinger straight at your
throat, and then(with a foot) makes a beeline for your crotch, that
would probably be a casual touch.  However, if the person is
nonchalantly tapping a foot against what they think is part of the
table but is, actually, your shin, well...in many cultures that is
considered a proposal of marriage and it's high time you excused
yourself so the mensfolk can discuss dowry young lady.
 
Second, if one is in doubt as to WHO it is doing that, is there any
polite or non-obtrusive way to find out?
 
Nothing could be simpler.  Just disappear under the table with your
food and smear some on every shoe.  But make sure you memorize what
food you put where.  Here's a tip:  try to establish some link
between the person's name and the food you smear on them.  For
example, if the person is named 'Gnocchi', smear sauerbraten, or
veal marsala.  If the person is named 'Calamari', smear pudding.
Then, after the round of footsie, all you need to do is excuse
yourself to the ladies' room, remove your stockings, and then taste
the food bits that have become attached.
 
Thirdly, what is the proper response if one wishes to give
encouragement, or if one wishes to NOT give encouragement?
 
To give encouragement:  Hook your one ankle over the side of the
table and your other behind your neck, roll your eyes upward and
scream, "DO ME BABY, DO ME DO ME DO ME!  *BARANGUS*!
WHEEEEEEEEEEEEEEEEEEEEEEEE!!!!!!!!!!!!!!!!!!!!!!!!!!
I MAKE MY OWN GRAVEEEEEEEEE!!!!!!!!!!!!!!!!!!!!!!!!!
WHEEEEEEEEEEEEEEEEEEEEEEEE!!!!!!!!!!!!!!!!!!!!!!!!!!"
 
To NOT give: Stab offending foot with a salad spoon.
 
And lastly, when is it appropriate, or a good idea, to initiate
proceedings oneself?
 
There are two schools of thought on this subject, both of
which I will ignore.  The best time to initiate contact is on a
heavy flow day.  But like I need to tell *you* that, you cutie.  It
is only inappropriate--no, not even then.  One subtle way of
initiating contact is to slide your instep behind the john's ankle,
raise his foot up to your hands, remove the trick's sock, slide
your panties aside and say to the waiter or waitress, "Yo!  Check
*this* shit out!"
 
There are other matters of ettiquette that I am also not
conversant with, but because of some recent incidents, I
find this particular one rather pressing at the moment, so to speak

Oh you are such a *button*!  I just wanna EAT YOU RIGHT UP!   Why
yes, they *are* Gold Toe socks I'm wearing.