These symbols merely indicate if the address has be active quite recently (within 30 days) or idle for more than a year.
Being recently active is potentially deceptive.
It could simply be Proof-of-Stake (on those coins with such income) happening on an unattended daemon wallet.
Or an otherwise idle address may have received some coins/payment from another address.
Addresses without symbols had their last activity in between those periods (more than 30 days but less than a year.)
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