Matthew 16:4
A wicked and adulterous generation demands ‘a sign’, but none will be given it except the sign of Jonah.” Then He left them and went away.
Mark 8:12
Jesus sighed deeply in His spirit and said, “Why does this generation demand a sign? Truly I tell you, no sign will be given to this generation.”
Luke 11:29
As the crowds were increasing, Jesus said, “This is a wicked generation. It demands a sign, but none will be given it except the sign of Jonah.
Argument by association. One of the weakest forms of argument.
When saints are buried, no one asks for them to be made incorruptible. They are found later, some times hundreds of years later. It is a sign, for us to study and imitate their life. But it is not a sign we asked for due to disbelief.
Your arguments that all incorruptibles can be explained by natural causes is what atheists use. Sorry if I assumed you were not a believer in Jesus Christ.