The S&P 500 ETF (SPY) - Get Report is stringing together a much-welcomed rally this week, up 0.8% Wednesday and 2.6% over the past three days. 

However, investors should keep an eye on shares of Cummins (CMI) - Get Report , TheStreet's Jim Cramer, co-manager of the Action Alerts PLUS portfolio, said on CNBC's "Stop Trading" segment. 

Shares of the diesel engine manufacturer are up 2.25% on the day and are up more than 5% from its 52-week lows made earlier this week. 

Cummins CMI data by YCharts

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This is one of the "bounce stocks" investors should watch closely over the next few days, Cramer explained. If it's able to piece together a sustainable rally, that could signal a bottom is in for other industrial, manufacturing, engineering companies. 

Cummins has a lot of exposure to China, so it could also indicate investors are changing their tune toward U.S.-based companies with exposure there. Cummins has a big share repurchase plan and a high quality balance sheet, too, Cramer said.

At the time of publication, Cramer's Action Alerts PLUS had no position in companies mentioned.