Here are SAL labels and surface mail labels from Zimbabwe.
SAL, or Surface Air Lifted, is a Universal Postal Union category of international mail service where mail is handled as surface mail in the country of origin, and the destination country, but as airmail between the two countries. This service is faster than surface mail while the cost is lower than airmail.(Wikipedia)
Year: ?, Gummed. Günter Mair's catalogue no: - ZIM-D-?, rouletted, sheets, black horizontal lines,
Year: ?, Gummed. Rouletted, sheets, black lines, bright green/white.