With regard to the comparison marker, a simile is mursal (explicitly marked) when the marker is mentioned and muʾakkad (emphatic or unmarked) when it is omitted.
Marked: “Zayd is brave like a lion.”
Unmarked: “Zayd is a lion.” The omitted marker presents the resemblance with greater force.
Deletion can intensify the apparent closeness of the terms, but context and grammatical structure are required before classifying a statement as emphatic simile rather than metaphor.