I think you and I both have a lot of similarities in our DC's. They don't sleep and want to nurse all the time! Don't worry if he's clingy...just means he's got a strong bond & is well-attached to you. It's a good thing actually (I have to remind myself of this sometimes!)
For nursing I use the sign for "milk" which is to open and close your hands like you're milking a cow. In fact DS uses that sign to mean "mom" too so it's kind of confusing sometimes--he'll sign milk when he wants me even if he doesn't want to nurse.
I'd suggest using a "code word" also...you don't want your toddler screaming "I want boobies!" in the middle of a store! DD used to call it "mommy meh" (her own invention) which is a little more subtle.
Don't feel like you have to give up nursing because he's having tantrums. Toddlers need to be taught nursing manners. I went to a sleep consultant for DD when she was around 18 months about her waking up all night to nurse (she did on demand during the day too, so I was going crazy nursing her like 8-12 times a day and not getting any sleep) and she said that this is actually developmentally a good age to start teaching them limits, that no, they can't have whatever they want, whenever they want. So yes, it does involve some tantrums and meltdowns (DD had some huge ones lasting like an hour or more), but it's actually good for them to start to learn about self-regulation, and it helps them in other areas too. She told me to pick one nursing session where you have time to deal with the inevitable tantrum at home (like don't pick right before bed or at the grocery, maybe sometime in the afternoon or some other session that you want to cut out). Then when your DC demands to nurse, you say, "No nursies (or whatever your word is) right now...it's not time to nurse." Then DC has a fit, you basically stay with them, hold them, talk to them, etc. and let the tantrum run its course. Then, at a later point (it could even be 10 min later, but it has to be after he stops tantruming and at a time that you pick, not him), you come in and say, "DC! It's nursing time! Time for milk!" and nurse him. That way he learns that there are times when he can't nurse, but you are not giving up on it altogether. Also, talk to him about no grabbing your shirt, etc. Only you can lift up your shirt or no nursing. And totally agree with HK, use distraction with sippy or snacks/treats. When that starts to work, then you can start to work on not nursing in public (when you don't want to). I used to do a LOT of nursing in the car before and after activities. And it took me at least 6 months before she would mostly sleep through the night.
It is a long process, but worth it if you have the patience to stick with it. For me it was worth it not to have to throw the baby out with the bath water and wean cold turkey. It feels gentler to me. DD kept nursing till age 3 and still does once in a while!
Don't worry about what the IL's think. It's none of their business. Don't let them (or pediatricians or spouse whoever) dictate what you do with nursing...it's between you and your DC only! Let me know if you want me to send you my copy of Nursing Mother's Guide to Weaning (or you can check it out from the library), it's helpful with a lot of tips even if you're not planning to wean right away.
Good luck!