Use of Δ (delta) to describe alkenes In a lot of (mainly older) papers discussing organic synthesis,  Δ is used to describe alkenes. As far as I know, this is no longer (if ever) IUPAC recommended nomenclature, so I haven't been able to find any reference to its intended use. 

The main area I'd seen it used was in steroid synthesis, where I assumed it had some specific use relating to that class of natural product (i.e. related to the biosynthesis etc.). However it does appear in other places, such as in the synthesis of Rifamycin: 


 Scheme from Nicolau Rapamycin synthesis. Taken from Classics in Total Synthesis I

"… the Δ35,36 double bond …" is used in the text to describe the alkene that gets reduced. Given that this could easily be referred to as the (E)-alkene or even just 206, I suspect that there is a special reason why Nicolau chose Δ35,36 however that reason isn't apparent to me.
@Loong's encyclopaedic knowledge of IUPAC nomenclature prompted me to have another look through the (irritatingly unsearchable) 2013 recommendations and the 2004 draft upon which they were built.
The only use of the uppercase Δ listed is when describing a double bond that links two cyclic systems:

P.28.2.2: Ring assemblies with a double bond junction
When two cyclic systems are linked by a double bond [...] the presence of a double bond is indicated by the Greek letter Δ, and the point of attachment of the ring is given by superscript locant numbers. This method is not continued in these recommendations

The example given is 1'1-bi(cyclopentylidene) (PIN) which should be used in preference of Δ1,1'-bicyclopentylidene.

Based on this, the example given in the question, using Δ to describe an unsaturated carbonyl would appear invalid, and used for convenience rather than to convey anything specific.