1989-93
In 1989, the 49ers' jerseys were further slightly altered with the stripes on the sleeves being made less bold and arranged closer together (sleeves on NFL jerseys began to get shorter and closer to the shoulder around this time). As for the team's helmet logo, black outlining on the intertwined "SF" was also added in 1989. For the 1990 season, concurrent with the rest of the teams in the NFL, the 49ers incorporated a small NFL Shield logo sewn on the bottom of the jersey's collar for the first time (this would be replaced with a redesigned "NFL Equipment" Shield logo for the 2002 season).
Prior to the 1991 season, the 49ers announced a prototype for a new logo and helmet design. Instead of the traditional "SF" oval, this new logo featured a stylized "49ers" in white with black and red shadows, along with a red facemask. However, fan reaction was so overwhelmingly negative that the idea was scrapped the next day. The only carryover from the 1991 planned uniform change (and the last significant change to the 1964-1995 uniform design) was the switch from red socks with three white stripes to solid red socks.
Read more about this topic: Logos And Uniforms Of The San Francisco 49ers