How to prove wallet ownership? Context
I would like to verify being A has access to a wallet and hence would like to ask them to pay a minimum amount to a particular wallet address owned by someone other than me, e.g. 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa, with a signature ThisIsUnexpected that I gave to the being A.
The basic concept I believe is quite simple, if being A agrees, they share with me their bitcoin wallet address:being_A_bitcoin_wallet_address. Next, I would share the expected signature, and selected recipient address (e.g. 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa) with being A. Being A then pays a minimal amount of bitcoin to 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa. After the transaction is completed, I look at the transaction history of the received donations to 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa and find the transaction made by being_A_bitcoin_wallet_address. Next, I look at the signature of that particular transaction and verify it reads: ThisIsUnexpected. If the transaction indeed has that signature I have a high certainty being A has access to being_A_bitcoin_wallet_address and I can verify their amount of funds.
Challenge
Though the idea may be relatively simple, I am experiencing some challenges in the execution.
To test the verification procedure, I thought I would look up the signatures of past transactions to that address. Hence I went to: https://www.blockchain.com/btc/address/1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa and looked at the list of transactions. At the moment of writing, this is the most recent transaction, so I thought I could perhaps take the Sigscript of the transaction (with index 1) and put it into this signature verification tool to get a human-readable signature. However that tool does not seem to provide a human-readable signature, nor do I know whether the arbitrary transaction I selected contains a &quot;Thank you Satoshi&quot;-like signature.
Question
How could I practically verify the signature of a bitcoin transaction (if it has one)?
Subquestions
I think this question could be segmented in the following sub-questions:

How can I verify that an arbitrary transaction contains a human-readable signature?
Which information of the transaction data should I use to obtain a human readable form of the transaction signature?
Which online resources could be used to verify a signature?
Is there a python script that provides a function: being_has_access_to_wallet(claimed_wallet_access_address, recipient_wallet_address,human_readable_signature, amount=0.0001) that returns True or False using something like a block explorer?
How can I verify that an arbitrary transaction contains a
human-readable signature?

There is no such thing as &quot;human-readable signature&quot;. The signature is just a very big number. Or we can treat it as a pair of very big numbers. Usually we encode it in hex, so it looks like 3044022007ae5e36b79303f992e153798061458b435d34285c5fddc20655451ac71b49f6022079421d162cad51db0daa0a934cbf5261d4b53f185604e9790094a49145f3812f01

Which information of the transaction data should I use to obtain a
human readable form of the transaction signature?

Input scripts

Which online resources could be used to verify a signature?

Google for &quot;ecdsa verify signature online&quot;. But I am not sure that these resources are suitable to verify bitcoin signatures.