German bunds are trying to deliver a message to stock-market investors: Achtung! According to market technician Tom McClellan, a narrowing yield spread between German 10-year bonds, known as bunds TMBMKDE-10Y, +1.09 and their U.S. counterpart TMUBMUSD10Y, +0.58 has historically been a bad omen for equity markets. The yield differential between bunds, which were carrying a negative yield about a year ago and reached a record spread—2.38 percentage points—on Dec. 28 with U.S. 10-year paper, has been on a tightening trend lately, illustrated by one McClellan chart (see below): via