Will the subscriber see that I have blocked them on WhatsApp - briefly?
No, a blocked contact will not be able to see your last seen or online status, nor will they receive any notifications when you come online or change your profile picture. However, they can still view messages and media sent before the block was imposed.
Will the subscriber see that I have blocked them on WhatsApp - in detail?
When you block someone on WhatsApp, they will not be able to see your online status or any changes in your profile picture. However, there are certain indications that may suggest to the blocked user that something has changed. For instance, if they try to send a message to you, it will show only one checkmark (indicating that the message was sent but not delivered), rather than two checkmarks (indicating that the message was both sent and received). Additionally, any calls made from their end will not go through, which might be another clue for them.
It's also important to note that if you have previously shared your status or profile picture with this person, they will still be able to see those updates until they clear their cache or delete the conversation from their device. This is because the media is stored locally on their phone.
In summary, while there are no explicit notifications sent to the blocked user informing them that they have been blocked, certain signs such as undelivered messages and failed calls may hint at the situation.