Another meaning of 同志 Is it true that 同志 has some different meaning? Like gay (as in homosexual) or something? I know that during the 20th century in China and communist Russia it was very common to call people 同志 (товарищ, comrade). So is it wrong to call someone 同志 in China nowadays?
Yes it is true. The official word for somebody who is gay is 同性恋者 (tóngxìngliànzhě), but in recent years 同志 (tóngzhì) is frequently used as slang for somebody who is gay.

From Baidu:


  1989年，香港人林奕华将自己筹划的首届同性恋电影节命名为《香港同志电影节》，这可能是这层意义的开端。（最晚是）从此开始，在中国大陆之外的中文地区，如台湾、香港、新加坡、马来西亚等，“同志”一词逐渐演变成对同性恋者的另一个称呼。用的时候并不是如“某某同志”这样作称谓用，而是“某某是一个同志”、“某某参加了一个同志团体”这样。这种用法起先在同性恋群体中使用，后来影响逐渐扩大，上述地区的社会各界都采纳了这个用法，例如台北市政府民政局就在《认识同志手册2001年版》中写道：“市长爱同志”。


The most relevant parts:


  1989年，香港人林奕华将自己筹划的首届同性恋电影节命名为《香港同志电影节》，这可能是这层意义的开端


In 1989, the Hongkonger 林奕华 named the first edition of his gay film festival "香港同志电影节"


  从此开始，在中国大陆之外的中文地区，如台湾、香港、新加坡、马来西亚等，“同志”一词逐渐演变成对同性恋者的另一个称呼。


From then on, in China and other Chinese speaking parts such as Taiwan, Hong kong, Singapore, Malaysia, “同志” gradually became the name for gays (and lesbians).

Further on the same page you can read:


  近年进入大陆后，由于绝大多数年轻人已经不再使用“同志”这个词汇，使得这层含义反而后来居上。


In recent years after the introduction in China most young people stopped to use the word “同志” due to its implicit meaning.

and


  尽管这一层新的含义在大陆地区也被越来越多的人所知晓并使用，不过中华人民共和国官方媒体和文件对这一外延含义基本不予采纳。


Despite its implicit meaning in China which is known and used my more and more people, the official Chinese media (in the mainland) and official documents don't accept this meaning.