user5152: To use a UTXO one must supply correct scriptSig or "unlocking script" to the given scriptPubKey "lock script", I know the scriptSig in PTPKH locking is sig and pubkey. My question is what makes the sig be unique to the specific UTXO ? 
It must be, otherwise I can take it and use it in different UTXO which has the same scriptPubKey .

user2306: No, because clients use SIGHASH_ALL in their transactions by default, which signs the outpoint you're spending in addition to the rest of the transaction.
People also sometimes add the flag SIGHASH_ANYONECANPAY to SIGHASH_ALL which still signs the outpoint you're spending.

5152: <p>To use a UTXO one must supply correct scriptSig or "unlocking script" to the given scriptPubKey "lock script", I know the scriptSig in PTPKH locking is sig and pubkey. My question is what makes the sig be unique to the specific UTXO ? 
It must be, otherwise I can take it and use it in different UTXO which has the same scriptPubKey .</p>
 2306: <p>No, because clients use <code>SIGHASH_ALL</code> in their transactions by default, which signs the outpoint you're spending in addition to the rest of the transaction.</p>

<p>People also sometimes add the flag <code>SIGHASH_ANYONECANPAY</code> to <code>SIGHASH_ALL</code> which still signs the outpoint you're spending.</p>
