Why touching like that?

My partner has when we are out in public chosen to put his hand at my neck, upper part of the back, touching. To me it is a touch that I am not all sure is suitable considering our surrounding? I don't know if it is me, or if this is his way of showing others (who they now may be, if even existing) she is mine, or what ever? Maybe I read too much into it? (He is working on his jealousy and I am trying to be supportive but it is at a point where I don't know what is normal or not, as far as this goes, as he has said he has always struggled with jealousy. I am only I believe a random looking woman. Never flirted or cheated, it is not something I have done wrong to cause it. Not in his opinion as well. ) What does this gesture mean?

Updates
9 mo
The reason I have not asked him what it means to him is because we come from different backgrounds and it can be tricky that way, I do not want it to be critique or him getting hurt over it. It could simple mean something good of course through and through and having nothing to do with jealousy. I have noticed some people reacting to it and not in a good way, more likely used to physical tenderness being shown other ways.
Why touching like that?
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