Making use of the Bima:
The Bima onto which the Sefer Torah is placed is considered Tashmishei Kedusha, and is therefore forbidden to be used for mundane purposes. If, however, the Sefer Torah is not directly placed onto the Bima, but rather is always placed on a cloth which is spread over the Bima, as is done today, then the Bima has a status of Tashmish Detashmishei Kedusha and may thus be used for mundane purposes. However, in such a case, the cloth which is designated to be placed over the table has the status of Tashmishei Kedusha and may not be used for mundane purposes. In all cases, it is permitted to stipulate on the Tashmishei Kedusha that it may be used for mundane matters. Furthermore, in a case that the custom is to allow using the Bima or its cloth for mundane matters, it is permitted to be done even if this stipulation was not explicitly made. Practically, based on this latter ruling, the custom is to make use of the Bima and its covering for mundane matters. [One may thus place Sefarim on top of the Bima, and may lean on it.] In all cases it is remains forbidden to use the Bima/cloth for a belittling purpose.
May one place a hat or glasses on the Bima?
May one bang on the Bima?
 Michaber 154/3 and 6 regarding chair of Sefer Torah which refers to the table which is on the Bima [M”B 154/10]; The Bima in 154/7 which is considered Kedushas Beis Hakenses refers to the elevated area that has the Bima of the Sefer Torah placed on it, and not to the Bima itself.
 M”B 154/6; Admur 42/4 regarding Tefillin case; 42/6 regarding all Tashmishei Kedusha items
 M”A 154/6; Beis Yosef 154; Machatzis Hashekel 154/6; P”M 153 M”Z 15; 154 A”A 6; Rama 154/6 and M”A 154/13 regarding the Paroches that it has a status of Kedushas Beis Hakneses and not Kedushas Aron being the Sefer Torah is never placed on it; see Piskeiy Teshuvos ibid footnote 158Maharshag 12; Kaf Hachaim 154/22; Tzedaka Umishpat 15 footnote 45; Piskeiy Teshuvos 154/4; See M”B 141/4 that one may lean on the table of the Bima,
If one sometimes places the Sefer Torah directly on the Bima: Then the Bima has a status of Tashmishei Kedusha, even though it is majority of the time used with a cloth. [M”A ibid; M”B 154/10; Shaar Hatziyon 154/8]
 Beis Yosef ibid; P”M 153 M”Z 15; Implication of Levush 154/3; M”B 154/6; See other opinions in Piskeiy Teshuvos 154/4
 See M”A 154/13; Poskim ibid
 Michaber 154/8; Admur 42/4 and 6
 Rama 154/8; Admur 42/6 in parentheses
The reason: As the custom makes it be considered as if a stipulation was made. [Admur ibid] This means as follows: Since the custom is to use it and it is impossible to beware from doing so, therefore Leiv Beis Din makes an initial stipulation in order so people do not stumble on this matter. Thus, even if a stipulation was not made, it is considered as if it was made. [Rama ibid]
 Rama ibid regarding table of the shul which seemingly refers to the Bima for Kerias Hatorah; Beis Yehuda 27; Az Nidbaru 3/49; Piskeiy Teshuvos 154/27; See however M”B 141/4-5
 Piskeiy Teshuvos 154/27; Poskim ibid; See however M”B 141/4-5 that one may not lean on the cloth that is on the Bima, see Piskeiy Teshuvos ibid footnote 158
 Admur 42/6
 As once the custom is to use it for mundane purposes we say Lev Beis Din Masneh and it hence does not have Kedusha.
 Az Nidbaru 3/49; Piskeiy Teshuvos 154/27 footnote 158
Seemingly the minhag is to permit banging on the bima in order to remind the congregation to recite Yaaleh V’yavo and similar insertions in davening. And this is not a belittling purpose, as it is for a mitzvah and there is no other way to communicate this information to the congregation due to the prohibition of making a verbal hefsek.