The 26-year-old had been a free agent ever since he was released by Queens Park Rangers at the end of last season.
"The fact that we've signed a player of Hogan's quality shows that players are looking at Wycombe in a different light now. He's a great attacking option to us and he has an ability on the ball which will stand out in League Two," manager Gareth Ainsworth told the club's official website.
"I want to add more goals to his game but the chances he creates will be a massive positive for us. Hogan is the type of player who can win a game with one moment of magic and I'm really excited to bring him here."
Meanwhile, Ephraim added: "I want to be in an atmosphere where I can smile when I'm playing and that's when I'm at my best. The manager and the chairman have given me the opportunity to do that here and I'm looking forward to it.
"I feel I can play anywhere across the midfield or up front, and I like to be creative. If I can bring that to the team and hopefully score a few goals then I'll be doing my job."
The winger, who has signed a contract until the end of the season, has been handed the number 31 shirt at Adams Park.