The postcards I believe you have are not issued by the Post office. They might be G Cachets. the cachet made by the Gateway Stamp company. The cachet can be Identified by a "G" with an arch over the top located at the bottom center area.
A Cachet is a design or inscription on an envelope to commemorate a postal or philatelic event. A collectible Baseball Cachet could include a players achievements, milestone, and record breaking accomplishments. A postal stamp and cancellation will coincide in date, or and relationship to commemorate the days event. Popular Cachets include Z Silk Cachets, and Gateway G silk Cachets. Cachets are also a popular item for players to sign.
The Earthquake G - Cachet dated Oct. 17, 1989 San Francisco Calif. Earthquake artwork, autographed by Manager Roger Craig is worth about $15. and unsigned about $7.50
The Game 3 G - Cachet dated Oct. 27, 1989 San Francisco Calif. Dave Stewrart cover, autographed by Stewart is worth $20., and unsigned $7.50
There were also 4 - San Francisco - Oakland series Cachets made by Z silk -Cachet that are worth about $20. Game 3 reads canceled by Eartquake below the silk artwork.
Part of the postal cancellation stamp reads Battle of the bay (Satiation) with the Official 1989 World Series logo
1989 World Series - 1989 was released on: USA: 14 October 1989
1989 World Series - 1989 Game 1 was released on: USA: 14 October 1989
1989 World Series - 1989 Game 3 was released on: USA: 27 October 1989
1989 World Series - 1989 Game 4 was released on: USA: 28 October 1989
The Oakland Athletics beat the SF Giants in the 1989 World Series.
The Oakland Athletics beat the San Fansisco Giants in the 1989 World Series.
Material World - TV series - was created in 1989.
In 1989, The UCLA Bruins won the College World Series. They went undefeated in this series. They finished their season with a record of 48-4.
There was a 10-day delay during the 1989 World Series due to an earthquake just prior to Game 3.
Phil Hellmuth.
Earthquake
1989