How can a security have a negative dividend amount?

There are four PERMNOs in the CRSP security universe with negative dividend amounts. 

In the 1920s, some companies required the payment of assessment fees from their shareholders. These assessment fees are recorded as negative dividend amounts and represent an obligation of the shareholders to make payments.  Two securities, Chicago Milwaukee St. Paul & Pacific (PERMNO 11228) and Wallace Murray Corp (PERMNO 15229) fall into that category.

Two other securities with negative dividend amounts are more recent:  British Airways PLC (PERMNO 71589) and BT Group PLC (PERMNO 66835).  These amounts have been verified as installment payments. 

CHICAGO MILWAUKEE ST PAUL & PAC
SIC: 400 (Railroads)
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PERMNO  DISTCD         DIVAMT              EXDT
11228         2844          -32.0600014        3/2/1928     

WALLACE MURRAY CORP
SIC: 3431 (Heating Equipment, Except Electric And Warm Air)
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PERMNO  DISTCD         DIVAMT              EXDT
15229         3260         -10.0000000       1/27/1927

BRITISH AIRWAYS PLC
Share code: 36
SIC: 4512 (Air Transportation Scheduled)
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PERMNO  DISTCD         DIVAMT              EXDT
71589         1282           -9.9200001         8/12/1987   

B T GROUP PLC
SIC: 4813 (Communications Services, Not Elsewhere Classified)
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PERMNO  DISTCD       DIVAMT               EXDT
66835        1280         -3.1080000          6/3/1985
66835        1280         -2.7387900          4/2/1986