In a note to clients, the analysts said that investors could be facing some "yellow lights" from "recently absolute weakness" in businesses like auto-parts suppliers, restaurants and hotels.

"Some parts of the consumer have been weak for a long time, while others are newfound and still too early to call the top," the analysts said.

However, they noted that this trend is not likely to weigh on the rest of the S&P 500, partly because of the current narrow breadth of the index. At the moment, the top 10 names in the S&P 500 make up more than 35% of it, a new record high, according to the BTIG analysts. 

"We call this the breadth paradox because the bigger of a weight these names become in the index, the less breadth matters, assuming these names continue to move higher," the analysts said. 

Information technology firms in particular make up much of the largest cohort of the S&P 500, leading the BTIG analysts to conclude that it is difficult to be too negative on the average until these stocks stop climbing.