There second foreshadow is Sanji being a cook. Yeah Sanji being a cook has a lot to do with fire. He has been seen using fire while cooking just like every cook and that’s why I think Oda did not make Sanji “Satan” since the beginning of the series but realised afterwards that his character/appearance would be really suitable for the role.
Moving on to the second part of this theory/speculation I am going to talk about Sanji’s Will and its former owner. Furthermore,I will talk about Sanji’s family. If Sanji really does resemble Satan , I firmly believe that he is the son of a Tenryubito. To be more specific,I believe that when the Tenryubito saw Sanji’s eyebrows (some months after being born cause babys’ heads are not completely formed when they are born)and maybe a tendency of him liking fire and approaching it , they understood/thought it was a sign from above. As most of us know, Satan protested against God and is said to have fought with him. So what the Celestial Dragons actually thought was that Sanji was going to destroy them as they are considered Gods-they thought he was a threat. Actually I believe he inherited Don Quixote Homing’s (Doffy’s father)will.