It depends on how people are saying it.
I grew up in the American south where people will say "bless her heart" or "bless your heart" or even "bless your little heart" and they're all condescending. It will come out like, "She's living on welfare because she had four babies by three different men, none of whom stuck around, bless her heart." Or "you really are particular about your food, bless your little heart." It's a way to sound socially acceptable but "everyone knows" what it really is for is to shame someone else in some way.
So look at the context in which people use it and, if you are able to pick up and interpret it, listen to the tone of voice they use when they say it. Also pay attention to how and when it's said to or about other people because it may be more obvious when it's applied to someone else other than yourself.
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"In the end, we decide if we're remembered for what happened to us or for what we did with it."
-- Randy K. Milholland
Avatar=WWI propaganda poster promoting victory gardens.