I don't know about the US but in Germany the context of things is definitely considered to judge if something is common or suspicious.
It's perfectly legal to own a clown mask and to wear it during carnival would be common. If you wear one outside carnival and walk towards the door of a bank, that's pretty suspicious.
It's perfectly legal to stand around in public. If you do it alone, at night in an area that's known to have many drug dealers and you suddenly start to run away if the police strolls along, then that's suspicious again.
And if the police considers you to be suspicious, they will ask what you're doing and to explain your behavior. They won't straight away throw you into jail obviously but they have the right to do a routine check.
For me, the cash in a regular package is really similar. If they seize your cash and you can proof that it was a weird way to pay for a car or that your aunt forgot her pile of cash when she visited you and you send it after her, then I'm quite sure, they'll have to hand it back. If you object to explain who sent you $10.000 and why, then I agree to find that pretty suspicious.
Assuming criminals do use FedEx etc. to transfer illegally earned money anonymously from one place to another, what would be the alternative to intervene? Or would you just let it happen?
Isn't that the fork's ring finger? Maybe it's demanding jewelry for compensation.