Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Issued | Type | Design | Serial format | Serials issued |
| --- | --- | --- | --- | --- |
| 1954.0 | Passenger | black on orange | AB 123 | unknown |
| 1955.0 | Passenger | yellow on blue | AB-123 | unknown |
| 1956.0 | Passenger | red on white | AB 123 | unknown |
| 1957.0 | Passenger | blue on white | AB 123 | unknown |
| 1958.0 | Passenger | black on yellow | AB 123 | unknown |
| 1959.0 | Passenger | green on white | AB 123 | unknown |
| 1960.0 | Passenger | white on red | AB 1234 | unknown |
| 1961.0 | Passenger | blue on yellow | AB 1234 | unknown |
| 1962.0 | Passenger | white on green | AB 1234 | unknown |
| 1963.0 | Passenger | black on white | AB 1234 | unknown |
| 1964.0 | Passenger | white on blue | AB-12-34 | AA-00-00 to HH-99-99 |
| 1965.0 | Passenger | red on white | AB-12-34 | JJ-00-00 to RR-99-99 |
| 1966.0 | Passenger | blue on white | AB-12-34 | SS-00-00 to ZZ-99-99 |
| 1967.0 | Passenger | green on white | AB-12-34 | AA-00-00 to HH-99-99 |
| 1968.0 | Passenger type 1 | white on green | AB-12-34 | JJ-00-00 to RR-99-99 |
| 1968.0 | Passenger type 2 | white on green | AB-12-34 | JJ-00-00 to RR-99-99 |
| 1969.0 | Passenger | yellow on blue | AB-12-34 | SS-00-00 to ZZ-99-99 |
| 1970.0 | Passenger | white on blue | AB-12-34 | AA-00-00 to HH-99-99 |
| 1971.0 | Passenger | white on green | AB-12-34 | JJ-00-00 to RR-99-99 |
| 1972.0 | Passenger | white on blue | AB-12-34 | SS-00-00 to ZZ-99-99 |
Question:
What was the issued serial for yellow on blue design issued in 1955?
Answer:
unknown