LONDON—Narrowing equity market breadth, rising volatility, and the prospects of rate hikes are the classic signs of a market top, BofA said in a weekly report on Thursday. Just five of the biggest U.S. technology stocks accounted for 71 percent of the nearly 20 percent gains in U.S stocks, BofA analysts noted of the performance of shares in a weekly flows note based on EPFR data. A situation in which a tiny group of stocks powers gains while others lose ground is often viewed as an indicator that a rally is running out of steam. The picture was equally worrying for world stocks, with year-to-date returns from a global index excluding the top 300 U.S. growth stocks at a paltry 1.6 percent despite a record-breaking $1 trillion of equity market inflows so far this year. Volatility gauges are also signaling caution. While U.S and European stock market volatility gauges have …