When you put objects in Amazon S3, what is the indication that an object was successfully stored? 

Each S3 account has a special bucket named_s3_logs. Success codes are written to this bucket with a timestamp and checksum. 

A success code is inserted into the S3 object metadata. 

A HTTP 200 result code and MD5 checksum, taken together, indicate that the operation was successful. 

Amazon S3 is engineered for 99.999999999% durability. Therefore, there is no need to confirm that data was inserted.