Strictly speaking, this question probably isn't appropriate for /r/AskHistorians because it deals with language instead of history. In the future, you should probably post questions like this to /r/Assyriology or PM me or another Assyriologist.

That said, Assyriologists use the plus-sign, +, to indicate ligatures of syllabograms. For example, i+na indicates that the two signs are written together as if they are a single sign. Similarly {d}EN.ZU is sometimes written dingir+EN.ZU, although this form appears as a ligature so often that it is generally understood with the standard notation.

An ex-sign, x, means the second sign is written inside the first. Since gur7 is a very complex sign, I am skeptical that it was written inside the ka, so the writing probably means KA+GUR7. ka.gur7 is a word (see edit below).

I'd need to see the full line to offer a translation, but KA means "mouth" and GUR7 means buru, "harvest."

This may be a mistaken reading for SAG GUR7 "the beginning of the harvest," but if the signs truly appears as written (GUR7+KA < *KAxGUR7) then it may be a condensed writing for "the harvest, summer" with a possessive (adverbial or adjectival) -ak suffix. This can occur, rarely, at the end of a line if the scribe ran out of space. But as I said, I'd need to see the full line to offer anything more than a guess.

Reference:

• Huehnergard, A Grammar of Akkadian (2000), 13.2 Logograms for a brief explanation of how to write ligatures.
• The Dictionary of Sumerian (ePSD) is the standard resource for translating Sumerian words.

To my knowledge, no one has studied the use of ligatures in any substantive way. They are not mentioned in either Von Soden or Labat.

EDIT:

• /u/farquier is right. There are 246 attestations of the spelling of KAGURUK [supervisor] as ka-guru7. I can't find a single attestation of the combined form, but this is almost certainly the reading you will want. The signs are probably just really close together.

According to the ePSD, KAxGUR7 can be read kugur(go to the search book, change the search field to "lexical", and input the ligature as KA*GUR7) but I can't seem to find that word. Un-ligatured KA.GUR7 is listed in the ePSD(look under "Sign-name") as kaguruk, "granary supervisor" and my inclination is to regard kugur as a variant form of kagurk. Are there any contextual clues in whatever text you're looking at that might suggest a plausible reading?