Burma Shave signs and copyright

Dear Rich: I'm an author writing and self-publishing a book of fiction. I would like to use an old Burma-Shave slogan, circa 1935, in my text. Burma-Shave was originally owned by Clinton Odell, sold to Phillip Morris in 1963 and then to American Safety Razor Company in 1997. The company is now in bankruptcy proceedings. It's an 18 word slogan: “Don’t pass cars/ On curve or hill/ If the cops don’t get you/ The morticians will/ Burma-Shave.”  The short answer: use it and don't worry. Burma Shave's use of sequential signs ended in 1963, coincidentally, the year in copyright history after which published works no longer required renewal. Putting aside issues as to whether posting the signs amounted to "publication," it's unlikely that signs like the one you want to use were registered and renewed. So, they're most likely public domain. In addition, the signs are arguably a short phrase, which is usually not protectible, and your use appears to be a fair use, anyway, since the incorporation in your novel would mostly likely be transformative.  Even if we're wrong about all of the preceding (sounds like a lawyer, now!), the party that acquires the Burma Shave rights in bankruptcy will probably not care about your use. In summary, "Our answer/Might seem way too long/But it's copyright/Not copy wrong."