Yes!!! What a great catch -- I love stuff like this, something no one apparently has noticed in all these years.
Sam Franklin is indeed the name of the painter that Dale Kingston meets at the gallery, and asks him for the time, as his alibi for the murder. Many will recognize the actor as Vic Tayback, or "Mel" from Mel's Diner in the TV show "Alice" (and the movie "Alice Doesn't Live Here Anymore").
"Suitable For Framing" was in Season 1.
And as you say, the signature "Sam Franklin" appears, in large block letters, on the painting behind Columbo in the hospital waiting room in "An Exercise in Fatality," from Season 4. I highly doubt it's a coincidence -- great inside joke!
Yes, in fact the Sam Franklin painting in the hospital appears to be the same as one that's displayed in Sam's gallery visit, from Season 1 -- or at least they're very similar (we don't get a good look at the same part of the canvas). So it looks like they recycled a "Suitable For Framing" prop in "Exercise In Fatality," just as some other props were re-used across different episodes.
Thank you Ted, nice to see some extra details filled in!
I hadn't realise this picture also appears in 'Suitable for Framing' - makes me think it's more likely to be just re-using a prop rather than anything more deliberate, but who knows?
Impressive attention to detail that they went to the length of signing a prop picture with the name of the artist character. On the other hand, I remember in that scene in 'Suitable for Framing' that Dale Kingston says something like "No matter how abstract the painting, he always signs his name realistically". I'd somehow never interpreted this comment as referring to Sam Franklin personally, but perhaps this is how it was intended. Maybe even at one stage they meant to give more prominence to Franklin's paintings in this episode, hence the signature being written in that way?
Franklin's repertoire seems somewhat diverse. This painting is fairly abstract, but elsewhere the episode we see him painting (presumably) a nude portrait, and when he arrives at the art viewing Kingston says something patronising like "You're the painter of these arid landscapes". It seems Franklin hasn't quite found his style and so can't break past the hospital market.